BMW OBD2 Wiki: Your Comprehensive Guide to Siemens MS43 ECU

The Siemens MS43 engine control unit (ECU) is a sophisticated system that manages the BMW M54 inline six-cylinder engine. Understanding this ECU is crucial for anyone involved in BMW diagnostics, repair, or performance tuning. This article serves as an in-depth guide, expanding upon the original documentation to provide a comprehensive Bmw Obd2 Wiki resource specifically focused on the MS43 ECU.

Understanding the MS43 ECU Architecture

The MS43 ECU, at the heart of many BMW models, employs an Infineon C167CR_SR CPU clocked at 24MHz. It utilizes a 4 megabit AMD AM29F400BB flash memory to store its critical software components. This memory is logically divided into distinct sections, each serving a specific purpose in the engine management system.

Memory Organization

The flash memory in the MS43 ECU is structured into three primary sections:

Bootloader & UIF (00000 – 0FFFF): This 64 kByte section houses the boot code, essential for ECU initialization and pre-program checks. It also contains the User Information Fields (UIF) and immobilizer data, which are written once during the ECU’s lifecycle.
Program Code (10000 – 7FFFF): The largest section at 384 kByte, this area contains the core operating program that dictates engine behavior and management strategies.
Calibration Data (70000 – 7FFFF): Occupying 64 kByte, this section stores crucial calibration parameters. These parameters are the configurable settings that the program code uses to control engine operation, including fuel maps, ignition timing, and various adaptation values.

Start	End	Section	Size
00000	0FFFF	Bootloader & UIF	64 kByte
10000	1FFFF	Program Code	384 kByte
20000	2FFFF	Program Code
30000	3FFFF	Program Code
40000	4FFFF	Program Code
50000	5FFFF	Program Code
60000	6FFFF	Program Code
70000	7FFFF	Calibration Data	64 kByte

Understanding the significance of each section is fundamental for advanced diagnostics and tuning. The bootloader ensures the ECU starts correctly, the program code dictates the operational logic, and the calibration data tailors the engine’s performance characteristics.

Checksum Verification for Data Integrity

To ensure the integrity of the data stored in the flash memory, the MS43 ECU employs checksums. These are crucial for detecting any data corruption that could lead to engine malfunctions or failure to start. The MS43 uses several types of checksums:

CRC16 Checksums: Three CRC16 checksums are used to validate the bootloader, program code, and calibration data sections individually.
32-bit Addition Checksums: Two 32-bit addition checksums verify the integrity of system monitoring parameters (_mon).

If any checksum fails, the ECU interprets this as flash memory corruption and will prevent engine startup, a critical safety feature.

Checksum Type	Location	Section
CRC16 Boot	0x3C24	Bootloader
CRC16 Program	0x6FDE0	Program Code
CRC16 Calibration	0x73FE0	Calibration
32-bit Addition Program	0x6FDAE	Program Code
32-bit Addition Calibration	0x72FFC	Calibration

Important Note: When correcting checksums, it’s vital to correct the addition checksums before the CRC16 checksums, as the addition checksums are calculated within the CRC16 protected areas.

Disabling Calibration Checksums (Advanced Users Only)

While generally not recommended due to the loss of data integrity verification, it’s possible to disable calibration checksums for advanced tuning or diagnostic purposes.

Disabling CRC16 Checksum:

Using a hex editor, set the Word at address 0x73FFE to 0xFFFF.
Set the Byte at address 0x6FFB0 to 0xA8.
Modify a specific byte in a firmware-dependent table (see table below) from 0x84 to 0x94.

Firmware	Location
430037	0x58999
430055	0x5B87D
430056	0x5B87F
430064	0x5FEB3
430066	0x63595
430069	0x63595

Disabling Monitor Checksum:

Warning: Disabling the monitor checksum, which is critical for the drive-by-wire safety system, is strongly discouraged.

TunerPro Method: Set the parameter lc_swi_cal_mon_cks to 165 (Hex).
Hexeditor Method: Modify a specific byte in a firmware-dependent table (see table below) to 0xA5.

Firmware	Location
430037	0x70CE3
430055	0x70D7C
430056	0x70D7E
430064	0x70DA0
430066	0x70E0A
430069	0x70E07

Variant Configuration: Adapting to Different BMW Models

The MS43 ECU is designed for use across various BMW chassis and models. To accommodate these differences, it utilizes a combination of configuration switches and automatic learning routines to adapt its functionality based on the vehicle’s specific features.

Configuration Switches

These switches are software parameters within the ECU that enable or disable specific functionalities based on the vehicle configuration.

c_conf_bts (Brake Light Test Switch Logic):
- 0: High signal = brake pedal pressed.
- 1: Low signal = brake pedal pressed.
c_conf_cat (Exhaust System Variant): Configures the lambda sensor setup and catalytic converter monitoring.
- 0: Auto-learn, single bank, 1 pre-cat sensor or CATV (SA199 – no O2 sensors).
- 1: Auto-learn, dual bank, 2 pre-cat sensors or CATV (SA199).
- 2: Single bank, 1 pre-cat, 1 post-cat sensor.
- 3: Dual bank, 2 pre-cat, 2 post-cat sensors.
- 4: Auto-learn, dual bank, with/without pre/post-cat sensors or CATV (SA199).
Important: After changing c_conf_cat, disconnect unused lambda sensors and clear “learned variants” adaptation to force ECU re-learning.
c_conf_cru_main_swi (Cruise Control Main Switch):
- 0: Main switch active, steering wheel button controlled.
- 1: Main switch inactive (Z3 usage), enabled with ignition voltage.
c_conf_dmtl (DMTL Module – Diagnostic Module Tank Leakage):
- 0: DMTL not present, function/diagnosis OFF.
- 1: DMTL present, function/diagnosis ON.
c_conf_ecf (Electrical Cooling Fan):
- 0: ECF not present, function/diagnosis OFF.
- 1: ECF present, function/diagnosis ON.
c_conf_ef (Exhaust Flap):
- 0: Exhaust flap not present, function/diagnosis OFF.
- 1: Exhaust flap present, function/diagnosis ON.
c_conf_mil (Diagnostic Lamp / MIL Variant – 2 Control & 2 Monitoring Sensors): Configures MIL illumination logic based on error type.
- 0: No MIL control, LV_MIL = 0.
- 1: Debounce after BMW error memory.
- 2: Debounce after OBDII error memory and component errors after 2nd drive cycle.
- 3: Debounce after OBDII error memory and CS-component error, immediate.
c_conf_mil_eu2 (Diagnostic Lamp / MIL Variant – 2 Control Sensors): Similar to c_conf_mil, but for EU2 emission standards.
- 0: No MIL control, LV_MIL = 0.
- 1: Debounce after BMW error memory.
- 2: Debounce after OBDII error memory and component errors after 2nd drive cycle.
- 3: Debounce after OBDII error memory and CS-component error, immediate.
c_conf_teg (Exhaust Gas Temperature Sensor):
- 0: Auto-learn EGT sensors.
- 1: No EGT sensors.
- 2: Dual bank, 4 EGT sensors.
Important: Clear “learned variants” adaptation to re-do EGT sensor learning.
c_conf_tq_lim_gear (Torque Limit First Gear):
- 0: First gear torque limiter inactive.
- 1: First gear torque limiter active (E53).
c_conf_sap (Secondary Air Pump):
- 0: Auto-learn SAP configuration.
- 1: SAP not present.
- 2: SAP present without SAFM (Secondary Air Flow Meter).
- 3: SAP present with SAFM.
Important: Clear “learned variants” adaptation to re-do SAP learning.

Automatic Variant Detection

The MS43 ECU also automatically detects certain vehicle features by monitoring CAN-bus messages.

Gearbox Variant:
- EGS1 CAN message: Automatic gearbox (at).
- SSG1 CAN message: Manual automatic gearbox (amt).
- No message: Manual gearbox (mt).
Important: Clear “learned variants” adaptation to re-do gearbox learning.
Air Condition System:
- INSTR3 CAN message: Air conditioning system present.
Important: Clear “learned variants” adaptation to re-do AC learning.
Steering Angle Sensor:
- LWS1 CAN message: Steering angle sensor present.
Important: Clear “learned variants” adaptation to re-do steering angle sensor learning.
Ignition Coil Type: Detects between 300g and pencil ignition coils.
- Checks pin X60002.12 connection to terminal 87.
- No connection: 300g coils.
- Connection: Pencil coils.
Important: Clear “learned variants” adaptation to re-do ignition coil learning. For older Index 03 ECUs with pencil coils, copy _pc_ ignition coil table values to _300_ counterparts.

Alt Text: Diagram showing pencil coil data for Siemens MS43 ECU, illustrating electrical parameters relevant to coil performance.

Ambient Pressure Sensor: Detects between Motorola and Infineon ambient pressure sensors.
- Checks voltage on sensor input pin against threshold c_v_var_amp.
- Voltage < c_v_var_amp: Motorola sensor.
- Voltage > c_v_var_amp: Infineon sensor.
- Detection result stored in boot sector (0x3EEC-0x3EF1): 0xA5 (Motorola), 0x5A (Infineon).
Note: Ambient sensor learning is typically one-time. Reset learning in boot mode by filling 0x3EEC-0x3EF1 with 0xFF.

Mass Air Flow (MAF) Sensor: Measuring Air Intake

The MAF sensor is a critical component for accurate engine management. It measures the amount of air entering the intake system, providing essential data for fuel and ignition calculations. The MS43 ECU uses a 0-5V MAF sensor signal, converting it to a kg/h reading.

Alt Text: TunerPro interface displaying M54B30 MAF scalar settings, highlighting parameters for mass airflow sensor calibration in BMW MS43 ECU.

MAF Sensor Scalars

The ECU utilizes scalars to convert the analog MAF sensor signal to a kg/h reading:

id_maf_tab: MAF Sensor Scalar 1×256 (voltage scale visualized).
id_saf_tab: Secondary Air MAF Sensor Scalar 1×256 (not used in production).
id_maf_tab__v_maf_1__v_maf_2: MAF Sensor Scalar 16×16 (numbered scale).
id_saf_tab__v_saf_1__v_saf_2: Secondary Air MAF Sensor Scalar 16×16 (not used in production).

Note: Voltage scale is inherent to ADC resolution and is visualized in 1×256 tables for better understanding. No interpolation is applied to table data.

MAF Sensor Input Monitoring

The ECU continuously monitors the MAF sensor voltage to diagnose potential issues:

c_maf_max_diag: Maximum voltage threshold for short-to-positive fault detection.
c_maf_min_diag: Minimum voltage threshold for short-to-ground fault detection.

If the voltage falls outside these thresholds, a MAF sensor error code is set, and MAF failsafe mode is activated. For engines with increased air intake capacity, c_maf_max_diag may need adjustment.

MAF Sensor Failsafe Mode

In case of MAF sensor failure, the ECU enters failsafe mode, substituting MAF sensor readings with values from the MAF diagnosis table:

ip_maf_1_diag__n__tps_av: MAF diagnosis table used as a load substitute.
- X axis: Throttle position sensor value (tps_av).
- Y axis: Engine speed (n).

This table is also used during normal operation for VANOS load filtering and diagnostics. Retuning this table is recommended for engines modified for increased airflow to maintain accurate load values.

Caution: The MAF substitute table is not a replacement for a functional MAF sensor and cannot fully account for all factors affecting engine breathing.

Engine Load Calculation: Key to Fuel and Ignition Control

The MS43 ECU calculates several filtered engine load parameters, crucial for fuel injection, ignition timing, and VANOS control. Key load parameters include:

Injection Load (maf_ti)
Ignition Load (maf_iga)
VANOS Load (maf_ivvt)

Important: Many logging tools report raw MAF sensor readings, which can differ significantly from these filtered loads, potentially misrepresenting actual engine operation. Accurate injection load monitoring is especially critical in boosted applications to prevent lean conditions.

Injection Load Filtering: Accounting for Volumetric Efficiency

The injection load calculation is a sophisticated process that accounts for variable valve overlap and volumetric efficiency changes. It’s essentially an optimized speed-density strategy.

Alt Text: Diagram illustrating Siemens MS43 intake manifold model, depicting air flow dynamics and volume calculations used for engine load determination.

Calculated Manifold Pressure:

The ECU calculates manifold absolute pressure using the ideal gas law, considering:

Effective intake manifold volume.
Engine speed.
MAF sensor airflow reading.
Volumetric efficiency (VO) tables.

The intake manifold volume is modeled differently for increasing and decreasing load scenarios, using four tables:

ip_vol_im__n__maf_mes: Increasing load, part/full load.
ip_vol_im_neg__n__maf_mes: Decreasing load, part/full load.
ip_vol_im_is__n__maf_mes: Increasing load, idle/trailing throttle/fuel cut-off.
ip_vol_im_neg_is__n__maf_mes: Decreasing load, idle/trailing throttle/fuel cut-off.

Volumetric Efficiency (VO) Calculation:

Eight VO lookup tables (ip_maf_vo_[1-8]__map__n) and a selection table (ip_nr_ip_maf__vo) determine the active VO table based on valve overlap. VO tables are pre-calculated speed-density tables representing air consumption per engine revolution at different speeds and pressures.

ip_nr_ip_maf__vo: Active VO table selection.
ip_maf_vo_[1-8]__map__n: VO tables for valve overlap steps 1-8.

The ECU interpolates load values between VO tables based on current valve overlap, providing a nuanced load calculation.

Note: Stock VO tables support manifold pressures up to 1250hPa. Boosted applications require extending the pressure axis of these tables.

Coolant Temperature Correction:

The output from VO tables is further corrected for coolant temperature effects on air density using the ip_maf_tco_cor__tco table.

VANOS Load Filtering: Stabilizing Load Readings

VANOS load is filtered using a weighting factor that blends MAF sensor readings with MAF substitute table values.

Alt Text: Graph depicting Vanos load weighting factor, showing the blending curve between MAF sensor and substitute table readings in Siemens MS43 ECU.

ip_fac_maf_sub_ivvt__maf_sub_diag: Weighting factor for maf_ivvt load.
ip_maf_1_diag__n__tps_av: MAF diagnosis table.

The weighting factor prioritizes MAF sensor readings at low loads and gradually shifts towards the MAF substitute table at higher loads, ensuring stable VANOS control even with fluctuating MAF readings. Retuning the MAF substitute table is advised for engines with increased airflow.

Extending VO Tables for Forced Induction

Forced induction systems can exceed the stock manifold pressure range (1250hPa). Extending the VO table pressure axis is crucial for accurate load calculation and proper ECU operation under boost.

VO tables can be extrapolated linearly above atmospheric pressure (~1000hPa). Extrapolate the last two pressure rows to the target boost pressure plus headroom for spikes and atmospheric variations. An Excel tool is available to assist with this extrapolation: File:Load Filtration Table Extrapolation.zip

Example VO tables for a 1500hPa boost target with 500hPa headroom:

Alt Text: Example of Siemens MS43 load filtration tables modified for boosted applications, showing extended pressure axis for accurate manifold pressure calculation under forced induction.

Note: These are starter tables; fine-tuning is required based on engine configuration. Verify calculated manifold pressure accuracy with a real MAP sensor. M50 manifold conversions may benefit from using Alpina B3S intake model values.

Fuel Injection: Precise Mixture Control

The MS43 fuel injection system utilizes maps based on engine load and speed to determine injection time (in milliseconds). Narrowband lambda sensors are used for closed-loop operation, with fuel trim learning affecting both closed and open loop fueling.

Key injection tables include:

ip_tipr_cst__tco: Pre cold start injection time basic value.
ip_ti_cst__n__tco: Cranking injection time basic value.

During normal operation, the ECU interpolates between cold and warm engine injection tables. Individual tables exist for each cylinder bank.

Cold Engine Injection Tables:

ip_ti_tco_1_is_ivvt__n__maf: Idle injection time, cold engine.
ip_ti_tco_1_pl_ivvt_1__n__maf: Bank 1 part load injection time, cold engine.
ip_ti_tco_1_pl_ivvt_2__n__maf: Bank 2 part load injection time, cold engine.

Warm Engine Injection Tables:

ip_ti_tco_2_is_ivvt__n__maf: Idle injection time, warm engine.
ip_ti_tco_2_pl_ivvt_1__n__maf: Bank 1 part load injection time, warm engine.
ip_ti_tco_2_pl_ivvt_2__n__maf: Bank 2 part load injection time, warm engine.

Axis Values (for injection tables):

X axis: Filtered engine load for injection (maf_ti).
Y axis: Engine speed (n).

Important: With a VANOS fault, the ECU uses the base injection time table ip_tib__n__maf. Update this table when tuning part-load tables.

Cold/Warm Engine Transition

Blending between cold and warm engine maps is controlled by transition maps:

ip_fac_is_ivvt__tco__tco_st: Idle coolant temperature blending factor.
ip_fac_pl_ivvt__tco__tco_st: Part/full load coolant temperature blending factor.

Axis Values (for transition tables):

X axis: Engine coolant temperature at start (tco_st).
Y axis: Current engine coolant temperature (tco).

Full Load Enrichment

During full load, part load injection time is multiplied by an enrichment factor from the ip_ti_fl table to achieve a richer air-fuel ratio for cooling and detonation prevention.

Viewing Full Load Enrichment as Lambda/AFR:

Alt Text: Full load injection enrichment table converted to lambda and AFR values in TunerPro, aiding in air-fuel ratio visualization for tuning Siemens MS43 ECU.

The ip_ti_fl__n table can be configured to display lambda or AFR values for easier tuning.

Warning: Accurate lambda/AFR values in the table depend on properly tuned part load injection tables for stoichiometric combustion (lambda 1.0).

Title	Conversion	Low Range	High Range
ip_ti_fl__n (Lambda)	1-(0.0039058823*X-0.5)	0.500	1.500
ip_ti_fl__n (AFR Gas)	14.7-(14.7(0.0039058823X-0.5))	7.409	22.050

Cat Preparation Lean-Out

In “cat preparation” or CATV state (no lambda sensors), part-load injection is leaned out using the ip_ti_cat_var__n__maf table.

Maximum Duty Cycle Considerations

Maximum duty cycle defines the maximum injector opening time at a given engine speed. Higher engine speeds reduce available injection time. Maintain a duty cycle below 90% for safety and injector performance. Full load enrichment should be factored into duty cycle calculations.

Alt Text: Maximum injection time calculator interface, a tool for determining safe injector duty cycle limits in Siemens MS43 engine tuning.

An Excel calculator is provided for duty cycle analysis: [File:Maximum Injection Time Calculator.zip](/index.php?title=File:Maximum Injection Time Calculator.zip “File:Maximum Injection Time Calculator.zip”)

Aftermarket Injector Scaling

Upgrading injectors requires adjustments to ECU parameters. Calculate a scaling factor based on the flow rate difference between stock and aftermarket injectors. Use the injection time multiplier t_ti_as_[cyl] for individual cylinder adjustments. Apply the scaling factor to fuel tables and reset the multiplier to 1.0.

Adjust injector-specific values:

c_ti_min_iv: Minimum injection time.
ip_ti_add_dly__vb: Injector dead time correction with battery voltage compensation.

Fuel Injector Deadtimes provides a list of suitable injectors and dead times.

Maps to scale for injector changes:

ip_tipr_cst__tco
ip_ti_cst__n__tco
ip_tib__n__maf
ip_ti_tco_1_is_ivvt__n__maf
ip_ti_tco_1_pl_ivvt_1__n__maf
ip_ti_tco_1_pl_ivvt_2__n__maf
ip_ti_tco_2_is_ivvt__n__maf
ip_ti_tco_2_pl_ivvt_1__n__maf
ip_ti_tco_2_pl_ivvt_2__n__maf
ip_ti_slow_wf_thd_min__tco
ip_ti_fast_wf_thd_min__tco

For fine-tuning after injector scaling, adjust lambda integrator values. For start and after-start behavior, adjust:

ip_ti_cast__tia__tco: Post-start enrichment factor.
ip_ti_cr_cst__cyc__tco: Gradual reduction of fuel enrichment at engine start.
ip_ti_cr_cast__cyc__tco: Gradual reduction of fuel enrichment after engine start.

Do not scale these factor maps directly to injector size.

Tip-In Enrichment / Cylinder Rewetting

The MS43 uses a sophisticated injection model to compensate for fuel film dynamics in the intake ports. This system includes:

Load-dependent wall film compensation: Based on injection time difference and wall film factor.
Throttle angle change compensation: For rapid load jumps, correcting for air path updating errors.

Relevant tables for wall film compensation:

ip_ti_pvs__pvs__n: PVS angle-dependent wall film amount.
ip_ti_tco_pos_wf__n__tco: Total wall film factor on acceleration.
ip_ti_tco_pos_fast_wf__n__tco: Total wall film factor on acceleration (high dynamic).
ip_ti_tco_neg_wf__n__tco: Total wall film factor on deceleration.
ip_ti_tco_neg_fast_wf__n__tco: Total wall film factor on deceleration (high dynamic).

Scale wall film tables based on AFR response during throttle release. Aim for lambda 1.0 (gasoline AFR 14.7). Decrease table values if AFR is too rich, increase if too lean. 5% step adjustments to ip_ti_pvs__pvs__n are a good starting point.

Correcting Fuel Consumption Gauge

Injector changes will affect fuel consumption readings. Correct the ip_fco_map_cor__pq_main_col table to recalibrate the fuel consumption gauge. If fuel tables are multiplied by a factor (e.g., 0.46), divide this table by the same factor. Fine-tuning can be done in the instrument cluster’s secret menu (Test 20).

Upgraded Fuel Pumps

For high-power applications, fuel pump upgrades may be necessary. The MS43 controls the fuel pump relay with time values:

c_t_efp_prev: Fuel pump relay time after ignition ON.
c_t_efp: Fuel pump relay delay after ignition OFF.

Slightly increasing these values may resolve starting issues with aftermarket pumps. Consider adding a check valve after pumps without integrated check valves to maintain stock-like cranking behavior.

Ignition System: Timing for Optimal Combustion

The MS43 ECU uses multiple ignition maps depending on engine state, temperature, and fuel quality. Main ignition tables for normal operation:

Cold Engine Ignition Tables:

ip_iga_tco_1_is_ivvt__n__maf: Idle ignition angle, cold engine.
ip_iga_tco_1_pl_ivvt__n__maf: Part/full load ignition angle, cold engine.

Warm Engine Ignition Tables:

ip_iga_tco_2_is_ivvt__n__maf: Idle ignition angle, warm engine.
ip_iga_ron_91_pl_ivvt__n__maf: Part/full load ignition angle for RON91 fuel, warm engine.
ip_iga_ron_98_pl_ivvt__n__maf: Part/full load ignition angle for RON98 fuel, warm engine.

Axis Values (for ignition tables):

X axis: Filtered engine load for ignition (maf_iga).
Y axis: Engine speed (n).

The ECU blends between cold and warm ignition maps based on coolant temperature, similar to injection blending. For warm engine operation, ignition timing is blended between RON91 and RON98 tables based on knock sensor feedback. Keep RON91 tables more conservative than RON98.

Catalyst heating (“_CH_” maps) retards ignition during warm-up. Anti-jerk (“_AJ_” maps) retards ignition during rapid throttle opening for smoother torque delivery. Anti-jerk can be disabled by increasing c_tco_min_aj to 142.5°C.

Ignition Current Feedback

MS43 monitors spark duration using a shunt resistor in the primary coil circuit. Aftermarket coils may trigger false “spark duration too short” or “no spark” DTCs.

Note: Early M52TU heads may have tight tolerances, causing coil mantle contact and short-circuiting the resistor. Isolate coils with Kapton tape or grind head aluminum for clearance.

c_tco_min_igcfb: Minimum coolant temperature for ignition diagnostic.
id_t_igcfb_min_300__n__maf: Minimum spark duration – screw type coils.
id_t_igcfb_min_pc__n__maf: Minimum spark duration – pencil type coils.
c_n_max_igcfb_diag: Minimum engine speed for ignition current feedback diagnostic.
c_cur_igc_max_diag: Maximum valid ignition current.
c_n_max_er: Maximum engine speed for misfire detection.

VANOS (Variable Valve Timing): Optimizing Valve Overlap

VANOS adjusts intake and exhaust camshaft timing for improved emissions, low-end torque, and high-end power. The MS43 controls dual VANOS independently, with a 40° crankshaft angle adjustment range.

Alt Text: VANOS minimum and maximum settings visualization, showing adjustable camshaft control parameters in Siemens MS43 engine management system.

VANOS uses hall sensors on intake and exhaust camshafts for position feedback. The intake sensor is static (works at 0 RPM), while the exhaust sensor is dynamic (requires minimum engine speed).

Main VANOS control maps for idle, part load, and full load:

Cold Engine VANOS Maps:

ip_cam_sp_tco_1_in_is__n__maf_ivvt: Intake camshaft setpoint, idle, cold engine.
ip_cam_sp_tco_1_ex_is__n__maf_ivvt: Exhaust camshaft setpoint, idle, cold engine.
ip_cam_sp_tco_1_in_pl__n__maf_ivvt: Intake camshaft setpoint, part load, cold engine.
ip_cam_sp_tco_1_ex_pl__n__maf_ivvt: Exhaust camshaft setpoint, part load, cold engine.
ip_cam_sp_tco_1_in_fl__n: Intake camshaft setpoint, full load, cold engine.
ip_cam_sp_tco_1_ex_fl__n: Exhaust camshaft setpoint, full load, cold engine.

Warm Engine VANOS Maps:

ip_cam_sp_tco_2_in_is__n__maf_ivvt: Intake camshaft setpoint, idle, warm engine.
ip_cam_sp_tco_2_ex_is__n__maf_ivvt: Exhaust camshaft setpoint, idle, warm engine.
ip_cam_sp_tco_2_in_pl__n__maf_ivvt: Intake camshaft setpoint, part load, warm engine.
ip_cam_sp_tco_2_ex_pl__n__maf_ivvt: Exhaust camshaft setpoint, part load, warm engine.
ip_cam_sp_tco_2_in_fl__n: Intake camshaft setpoint, full load, warm engine.
ip_cam_sp_tco_2_ex_fl__n: Exhaust camshaft setpoint, full load, warm engine.

Axis Values (for VANOS tables):

X axis: Filtered engine load for VANOS (maf_ivvt).
Y axis: Engine speed (n).

Cold/warm map blending for VANOS is controlled by:

ip_fac_cam_sp_in_is__tco__tco_st: Intake camshaft idle blending factor.
ip_fac_cam_sp_ex_is__tco__tco_st: Exhaust camshaft idle blending factor.
ip_fac_cam_sp_in_pl__tco__tco_st: Intake camshaft part load blending factor.
ip_fac_cam_sp_ex_pl__tco__tco_st: Exhaust camshaft part load blending factor.

Axis Values (for VANOS blending tables):

X axis: Engine coolant temperature at start (tco_st).
Y axis: Current engine coolant temperature (tco).

Camshaft Parameters

MS43 uses parameters to define camshaft specifications for proper VANOS control and diagnostics.

Intake Camshaft Parameters:

c_cam_op_in: Intake camshaft duration (degrees).
c_cam_adj_rng_max_in: Intake camshaft max VANOS adjustment range.
c_cam_ini_in: Intake camshaft reference angle initialization.
c_cor_cam_in_ref: Intake camshaft edge CRK-correction (intake lobe centerline).

Exhaust Camshaft Parameters:

c_cam_op_ex: Exhaust camshaft duration (degrees).
c_cam_adj_rng_max_ex: Exhaust camshaft max VANOS adjustment range.
c_cam_ini_ex: Exhaust camshaft reference angle initialization.
c_cor_cam_ex_ref: Exhaust camshaft edge CRK-correction (exhaust lobe centerline).

Calibrate VANOS setpoint tables according to camshaft values. The B30 intake camshaft is 6° more advanced than other M52TU/M54 intake cams, improving top-end power.

VANOS setpoint range example (B30 intake):

Upper Limit: c_cam_ini_in/ex (126°)
Lower Limit: c_cam_ini_in/ex - c_cam_adj_rng_max_in/ex (126° – 40° = 86°)

Drive-By-Wire System: Electronic Throttle Control

The MS43 employs a Drive-By-Wire (DBW) system, using both the throttle valve and idle control valve for air intake management. Accelerator pedal units differ between manual and automatic transmissions, with automatic versions including a kick-down switch simulation.

Drivers Wish Tables

The ECU uses Drivers Wish tables to translate accelerator pedal input (PVS) into throttle and idle control valve actions.

Alt Text: TunerPro comparison view of drivers wish tables ip_tps_sp_pvs and ip_isapwm_pvs, illustrating throttle and idle control valve mapping in Siemens MS43 ECU.

ip_tps_sp_pvs: Throttle valve opening for a given PVS input.
ip_isapwm_pvs: Idle control valve duty cycle for a given PVS input.

Stock setup prioritizes idle control valve for airflow control at low PVS inputs (0-15°) and switches to throttle valve control at higher inputs.

Drivers Wish Dashpot

Dashpot function smooths throttle release by limiting the rate of PVS input decrease.

ip_pvs_dif_neg_fac & ip_pvs_dif_cr_neg: Dashpot correction factors based on PVS input difference.

The dashpot correction decays over time, providing a smooth transition. Dashpot function can be disabled when the clutch is pressed by setting lc_dhp_ltc to 1.

Drivers Wish Input Correction

Input correction smooths part-load driving by limiting the rate of PVS input increase.

ip_pvs_cor_max_rpl_[gear]: PVS input increase limitation threshold.
ip_pvs_cor_rpl_lgrd_[gear]: PVS input increase increment value.
ip_t_pvs_cor_rpl_[gear]: Limitation duration.

Limitation is bypassed under conditions like decreasing PVS input, high PVS input change gradient, clutch pressed, or high PVS input value. Disable input correction by setting c_pvs_cor_max_rpl or c_pvs_av_grd_max_rpl to zero.

Throttle Request Correction

Throttle request correction limits throttle closing rate based on engine load for smoother driving.

c_tps_req_ltc_min: Minimum throttle setpoint for correction activation.
ip_tps_req_ltc_min_[gear]: Gear-dependent minimum throttle setpoint.
ip_tps_req_ltc_lgrd_[gear]: Throttle setpoint decrement value.
ip_t_tps_req_ltc_max_[gear]: Limitation duration.
id_tps_req_ltc_gear_[gearbox]: Gearbox-dependent throttle request correction activation.

Disable throttle request correction by setting id_tps_req_ltc_gear_[gearbox] tables to zero.

Torque Management: Limiting Engine Output

MS43 estimates engine torque using static torque models:

ip_tqi_pvs__n__pvs: Indexed engine torque (PVS).
ip_tqi_maf__n__maf: Indexed engine torque (MAF).
ip_tqfr__n__maf: Frictional torque losses (MAF).

Torque Limiting

The ECU limits engine torque to the maximum allowed value defined in ip_tq_max__n__pvs_cor_rpl. For modified engines, torque models may cause unexpected power reductions. Disable torque limiting by setting ip_tq_max__n__pvs_cor_rpl values to 65535 Nm.

First gear torque limiting (E53 X5) is enabled by setting c_conf_tq_lim_gear to 1 and is controlled by c_tq_max_gear.

Idlespeed Control: Maintaining Stable Idle

MS43 uses several tables to define nominal idle speed:

ip_n_sp_is: Nominal idle speed (no load).
ip_dri_n_sp_is: Nominal idle speed (drive engaged, AT).
ip_acin_n_sp_is: Nominal idle speed (AC ON).
ip_dri_acin_n_sp_is: Nominal idle speed (AC ON, drive engaged, AT).

Idle speed is further adjusted by:

ip_n_sp_add_cha_cdn_bat: Battery charge state offset.
ip_n_sp_add_heat: Catalyst heating offset.

Idle speed change rate is controlled by c_n_sp_lgrd_is.

Full Load Operation: Maximizing Performance

During full load, the ECU enriches fuel mixture and disables closed-loop lambda correction to prevent knock and control combustion temperature. Learned fuel trims remain active.

Alt Text: Full load operation diagram in TunerPro, outlining tables and parameters active during high engine load conditions in Siemens MS43 ECU.

Full Load Activation

Full load activation is determined by:

Engine speed > c_n_min_fl.
Accelerator pedal position exceeding thresholds in:
- id_pvs_fl__n: Injection full load threshold.
- id_pvs_fl_ivvt__n: VANOS full load threshold.
- id_pvs_fl_vim__n_vim: DISA full load threshold.
AC compressor disengagement threshold: c_pvs_fl_accin.

Full load activation is delayed after engine start until either:

Vehicle speed > c_vs_min_fl.
Coolant temperature > c_tco_min_fl.

Full Load Effects

Full load operation switches VANOS and DISA to dedicated full load tables and applies a fuel enrichment factor.

ip_ti_fl__n: Full load injection enrichment factor.
ip_cam_sp_tco_1/2_in/ex_fl__n: Full load VANOS setpoint tables (cold/warm engine, intake/exhaust).
id_vim_fl__n_vim: Full load DISA activation setpoints.

Time Limited Full Load (Potentially Unused)

MS43 has gear-dependent timers to limit full load duration.

id_t_max_fl__gear (MT) / id_t_max_fl_at__gear (AT): Max full load time per gear.
c_n_max_fl: Max engine speed for time-limited full load.
c_vs_max_fl: Max vehicle speed for time-limited full load activation (disabled in production).

Lambda Regulation: Closed-Loop Air-Fuel Control

MS43 uses cylinder bank-selective lambda regulation with narrowband O2 sensors, aiming for stoichiometric combustion (lambda 1.0, 14.7 AFR) in closed loop.

Alt Text: Lambda adaptation scheme diagram, illustrating the closed-loop fuel control process and adaptation mechanisms in Siemens MS43 ECU.

Closed Loop Requirements

Closed loop mode activation requires:

Engine speed > c_lam_n_min.
Time after start > id_t_max_ls__tco_st.
Coolant temperature > id_lam_tco_min__tco_st.

Lambda integrators (short-term fuel trims – STFT) regulate mixture within limits:

c_lam_min: Minimum lambda integrator value (lean limit).
c_lam_max: Maximum lambda integrator value (rich limit).

Lambda Adaptation (Fuel Trims)

Additive and multiplicative adaptation corrections (long-term fuel trims – LTFT) are applied across the entire fuel map. Adaptation values are attenuated at lower engine temperatures using:

ip_ti_ad_fac_fac__tco__ti_ad_fac: Multiplicative component weighting.
ip_ti_ad_add_fac__tco__ti_ad_add: Additive component weighting.

Main Adaptation Conditions:

c_tco_ti_ad_min: Minimum coolant temperature for adaptation.
c_tia_ti_ad_max: Maximum intake air temperature for adaptation.
c_maf_ti_ad_max: Maximum air mass for adaptation.

Lambda Additive Correction Limits:

c_ti_ad_add_min/max: Additive factor limits.
c_maf_ti_ad_add_max: Max air mass for additive adaptation.
c_n_ti_ad_add_max: Max engine speed for additive adaptation.

Lambda Multiplicative Correction Limits:

c_ti_ad_fac_min/max: Multiplicative factor limits.
c_n_ti_ad_fac_min: Min engine speed for multiplicative adaptation.
c_maf_ti_ad_fac_min: Min air mass for multiplicative adaptation.
ip_maf_ti_ad_min/max__n: Min/max air mass for multiplicative adaptation.

Disable fuel trims temporarily by setting c_tco_ti_ad_min to a high value (e.g., 140°C). Cylinder-individual fuel trims (disabled by setting c_n_max_cyl_lam to 0) can be problematic with non-stock exhaust manifolds.

Diagnostic Trouble Codes (DTC): Error Detection

MS43 performs self-diagnostic tests and uses a debounce system to prevent transient errors from triggering DTCs.

DTC to P-Code Translation

MS43 translates internal DTCs to OBD2 P-codes using variables like c_dtc_[dtc name]_x. Diagnostic Trouble Code Translation lists DTCs and their P-code equivalents.

Suppressing DTCs

Suppressible DTCs use incrementation (c_abc_inc_[dtc name]) and threshold (c_abc_max_[dtc name]) variables for debouncing. Suppress DTCs by setting the corresponding c_abc_inc_[dtc name] to zero. Caution: Suppressing DTCs disables associated functions; address the underlying issue instead.

Extra Features and Modifications

Engine Coolant Temperature Control

MS43 controls an electronic thermostat to adjust coolant temperature based on various conditions.

E-thermostat Minimum Conditions:

c_tam_min_ect, c_tia_min_ect, c_toil_min_ect, c_tco_min_ect: Minimum temperature thresholds for e-thermostat activation.

E-thermostat Maximum Conditions:

c_tia_max_ect, c_tco_ex_max_ect, c_toil_max_ect: Maximum temperature thresholds, triggering target coolant temperature adjustments.

E-thermostat Target Coolant Temperatures:

c_tco_sp_toil_min, c_tco_sp_tco_ex_max, c_tco_sp_tia_max, c_tco_bol_ect: Target coolant temperatures based on different conditions.

E-thermostat Target Coolant Temperature Maps:

id_tco_sp_ect__n__maf_sub, id_tco_sp_ect_acin__n__maf_sub: Target coolant temperature maps (AC off/on).

E-thermostat Regulations:

ip_ectpwm_i__tco_dif, ip_ectpwm_p__tco_dif, id_ectpwm_add__n__tco_sp: E-thermostat PID control parameters.

Alt Text: TunerPro depiction of coolant temperature control maps in Siemens MS43 ECU, showing parameters for electronic thermostat management.

Electronic Coolant Fan Control

MS43 controls the cooling fan via PWM based on exhaust temperature, radiator outlet temperature, AC demand, and vehicle speed.

ip_n_ecf__tco_ex: Fan speed vs. radiator outlet temperature.
ip_n_ecf_temp_cat__temp_cat: Fan speed vs. catalyst temperature.
id_n_ecf_min_accin__n_ecf: Fan speed CAN-bus request.
ip_n_ecf_vs_cor__vs: Vehicle speed correction for fan speed.

Secondary Air Pump (SAP) Removal

Disable SAP by setting c_conf_sap to 1 and clearing “learned variants” adaptation.

MAF Sensor Scalar Adjustments

MAF sensor scalars convert analog voltage to kg/h airflow. M54B22/B25 and M54B30 MAF sensors have different flow characteristics. Aftermarket slot-type sensors (Ford, Bosch) are often used in high-horsepower turbo setups. Factory airflow limit is 1024 kg/h (patchable to double). Max engine load is 1389 mg/stroke.

id_maf_tab__v_maf_1__v_maf_2 (1×256) & id_maf_tab (16×16): MAF sensor definition tables.

Engine Speed Limiter (Rev Limiter)

MS43 has gear-dependent soft and hard rev limiters for manual (MT) and automatic (AT) transmissions. Soft limiter cuts injectors, hard limiter cuts all cylinders.

id_n_max_at/mt: Soft limiter for AT/MT.
id_n_max_max_at/mt: Hard limiter for AT/MT.
id_n_max_vs_max_at/mt__gear: Speed-dependent soft limiter disable threshold.
c_n_max_vs_diag: RPM limiter for missing vehicle speed signal.

Aggressive hard cut can be achieved by reducing limiter hysteresis: c_n_max_hys to 0 and c_n_max_hys_max to 32.

Vehicle Speed Limiter

Vehicle speed limiter has soft and hard stages. Soft limiter cuts cylinders, hard limiter cuts fuel pump.

c_vs_max_at/mt_1: Soft limiter thresholds for AT/MT.
c_vs_max_add: Hard limiter offset. ov_vs_max_max = c_vs_max_[at/mt]_1 + c_vs_max_add.

Increase speed limit by maxing out c_vs_max_[at/mt]_1 and c_vs_max_add (up to 287 km/h). Disable speed limiter completely by setting c_n_min_vs_max to 8160 RPM.

c_n_min_vs_max: Minimum engine speed for vehicle speed limiter activation.
c_vs_max_toil_max: Speed limit for max oil temperature.
c_vs_max_amt: Speed limit for active SSG error.

Safety Features (Handle with Care)

Catalyst Overheating Prevention (COP)

ip_maf_min_cop__n__iga_dif & ip_maf_min_cop_ron__n__iga_dif: MAF thresholds for COP activation (normal/bad fuel).

Disable COP by setting these tables to 1389 mg/stroke.

CAT Heating

id_t_ch_ti_cat_var__tco_st & ip_t_ch_ti__tco_st__km_ctr: Injection time correction duration for CAT heating.
id_t_iga_ch_cat_var__tco_st & ip_t_iga_ch__tco_st__km_ctr: Ignition angle intervention duration for CAT heating.

Disable CAT heating by setting these tables to 0.

Misfire Detection

c_n_min_er & c_n_max_er: Min/max engine speed for misfire detection.

Knock Detection

MS43 samples knock sensor voltage and uses thresholds to detect level 1 (light) and level 2 (heavy) knock.

id_knkwb_[0-5] & id_knkwe_[0-5]: Knock measurement window tables.
ip_fac_knk_[0-5]: Level 1 knock threshold factors.
id_fac_knks_thd__tia: Level 2 knock threshold factor.
id_iga_dec_knk_1/2__n: Ignition angle retard for level 1/2 knock.

Reduce multiplication factors to increase knock detection sensitivity, increase to decrease sensitivity. Sustained knock retard fades in RON91 ignition table over RON98 table.

Special Functions and Modifications

Differential Vehicle Speed Sensor Mod for E30/E34

For using MS43 in older chassis (E30/E34) with differential speed sensor, adjust:

c_vs_fac: Vehicle speed sensor pulses per kilometer (E30/E34/E36: ~1096-1100).

Exhaust Pop Modifications

Toggleable Exhaust Pops: Disable trailing throttle fuel cut by raising minimum engine speed threshold in:

ip_n_min_puc__tco (AC off) & ip_n_min_accin_puc__tco (AC on).

Tune pop intensity with ignition tables:

ip_iga_pu__n__tco, ip_iga_puc__n__tco, ip_iga_accin_puc__n__tco.

Alt Text: TunerPro depiction of toggleable exhaust pops setup, showing parameter adjustments for creating on-demand exhaust sound effects in Siemens MS43 ECU.

Timered Exhaust Pops: Delay trailing throttle fuel cut activation:

c_t_puc_deacc_vs: Delay when stationary.
ip_t_puc_deacc_1-5__n__maf_mmv: Gear-dependent delays.

Tune pop intensity with the same ignition tables as toggleable pops.

Alt Text: TunerPro depiction of timered exhaust pops configuration, showcasing parameter settings for achieving controlled duration exhaust pops in Siemens MS43 ECU.

Combined Approach: Use both toggleable and timered methods for different pop behaviors with AC on/off.

Alt Text: TunerPro depiction of combined exhaust pops setup, showing parameter settings for varied exhaust pop behavior based on AC state in Siemens MS43 ECU.

Idle Control Valve (ICV) Delete

ICV delete is possible due to the motorized throttle body. Disconnect ICV, plug intake manifold hole (preferred).

Alt Text: TunerPro ICV delete configuration interface, highlighting ip_pvs_isa_isapwm table adjustments for removing idle control valve in Siemens MS43 ECU.

Rescale ip_pvs_isa_isapwm table to emulate ICV airflow with the electronic throttle. Copyable ICV Delete Tables M54B30 ONLY!. Adjust table values for M54B22/B25 based on throttle body size difference.

Lumpy Idle / Fake Race Camshafts

Simulate race camshaft idle sound by increasing valve overlap via VANOS adjustments. Adjust idle speed VANOS setpoints in:

ip_cam_sp_tco_1/2_in/ex_is__n__maf_iv.

Raise misfire detection threshold c_n_min_er above desired idle speed. Max valve overlap is achieved with lowest intake (86°) and exhaust (-80°) VANOS values.

Alt Text: TunerPro depiction of camshaft modification settings, showcasing VANOS parameter adjustments for simulating lumpy idle in Siemens MS43 ECU.

Map Reduction

Reduce the number of tuning maps by forcing ECU to use cold engine (tco_1) tables. Set transition tables to “1.0”:

ip_fac_is_ivvt, ip_fac_pl_ivvt, ip_fac_cam_sp_in/ex_is/pl.

Alt Text: MS43 map reduction diagram in TunerPro, illustrating the simplification of tuning maps by using cold engine tables in Siemens MS43 ECU.

Tune fallback tables ip_tib__n__maf, ip_igab_is__n__maf, ip_igab__n__maf.

VANOS Tweak for Midrange Power

Insert provided VANOS tables into part-load maps for improved midrange power. Tables optimized for M54B30 engine. Adjust for different engine configurations and exhaust setups.

Tuning for Turbocharged Applications

Key maps for turbocharged MS43 tuning:

Map	Value
c_abc_inc_vim	0
c_conf_cat	0
c_maf_max_diag	2048
ldpm_maf_8	35 \| 75 \| 125 \| 175 \| 250 \| 325 \| 400 \| 450 \| 550 \| 700 \| 950 \| 1250
ldpm_maf_iga_1	50 \| 75 \| 125 \| 175 \| 250 \| 325 \| 400 \| 500 \| 600 \| 700 \| 950 \| 1350
ldpm_maf_iga_2	50 \| 75 \| 100 \| 125 \| 175 \| 250 \| 300 \| 325 \| 400 \| 500 \| 600 \| 700 \| 850 \| 1000 \| 1150 \| 1350
ldpm_maf_mes_1	76 \| 125 \| 272 \| 376 \| 523 \| 1002
ldpm_map_1	100 \| 200 \| 300 \| 600 \| 900 \| 1050 \| 1250 \| 2000
ldpm_n_11	600 \| 1000 \| 1200 \| 1500 \| 1600 \| 2000 \| 2500 \| 3000 \| 3500 \| 3900 \| 4100 \| 4500 \| 4800 \| 5500 \| 6300 \| 7000
ldpm_n_14	320 \| 600 \| 900 \| 1000 \| 1200 \| 1500 \| 1600 \| 2000 \| 2250 \| 2500 \| 3000 \| 3500 \| 3900 \| 4100 \| 4500 \| 4800 \| 5100 \| 5500 \| 6300 \| 7000
ldpm_n_4	600 \| 1000 \| 1200 \| 1500 \| 1600 \| 2000 \| 2500 \| 3000 \| 3500 \| 3900 \| 4100 \| 4500 \| 4800 \| 5500 \| 6300 \| 7000
id_maf_tab	Varies by maf
ip_ti_fl__n	0.016
ip_iga_ron_91_pl_ivvt__n__maf	Decrease above 500mg/stk
ip_iga_ron_98_pl_ivvt__n__maf	Decrease above 500mg/stk
ip_maf_min_cop__n__iga_dif	1389
ip_maf_min_cop_ron__n__iga_dif	1389
ip_ti_cop_nr_1_1__n__maf	0
ip_ti_cop_nr_1_2__n__maf	0
ip_ti_cop_nr_2_1__n__maf	0
ip_ti_cop_nr_2_2__n__maf	0
ip_ti_cop_nr_3_1__n__maf	0
ip_ti_cop_nr_3_2__n__maf	0
ip_ti_cop_nr_4_1__n__maf	0
ip_ti_cop_nr_4_2__n__maf	0
ip_ti_cop_nr_5_1__n__maf	0
ip_ti_cop_nr_5_2__n__maf	0

Consider extending load filtration, aftermarket injector scaling, and forced induction upgrades as described in dedicated sections of this BMW OBD2 wiki resource.