For automotive enthusiasts and professionals alike, understanding how to access vehicle data is crucial. The SAE J1979 standard is a cornerstone in this domain, particularly when it comes to On-Board Diagnostics (OBD2) systems. This standard, essential for accessing Electronic Control Unit (ECU) parameters, is especially relevant to vehicles like the BA Falcon. Let’s delve into the world of J1979 and OBD2, and explore how it unlocks valuable insights from your car’s computer.
SAE J1979, established by the Environmental Protection Agency (EPA), defines a standardized way to request and receive diagnostic information from a vehicle’s ECU. It outlines the first nine ‘Modes’ of operation for retrieving data, and specifies the ‘Parameter IDs’ (PIDs) used within Mode 01 for accessing live data. These modes are fundamental to any OBD2 diagnostic process and provide a structured approach to vehicle communication.
Here’s a breakdown of the standard OBD2 Modes as defined by J1979:
- $01 – Show current data: Displays real-time data parameters from the engine and related systems.
- $02 – Show freeze frame data: Presents a snapshot of data parameters recorded at the moment a Diagnostic Trouble Code (DTC) was set.
- $03 – Show stored trouble codes: Retrieves a list of current DTCs that are actively triggering the check engine light.
- $04 – Clear trouble codes and stored values: Resets DTCs and clears related stored data. Use with caution and only after addressing the underlying issue.
- $05 – Test results, oxygen sensors: Accesses results from oxygen sensor monitoring tests.
- $06 – Test results, non-continuously monitored: Provides results for on-demand diagnostic tests.
- $07 – Show pending trouble codes: Displays DTCs that have been detected but haven’t yet triggered the check engine light.
- $08 – Special control mode: Allows for bi-directional control of certain vehicle systems for testing purposes.
- $09 – Request vehicle information: Retrieves vehicle-specific information such as VIN, calibration IDs, and more.
Mode $01, focused on showing current data, offers access to a wide range of parameters. While the OBD2 standard allows for up to 254 PIDs, J1979 initially defined the first 30 (PID $00 to $1F). PID $00 is particularly important as it indicates which PIDs within the $01 to $1F range are actually supported by the vehicle’s ECU. This support is communicated in a bitwise fashion, allowing a scantool to quickly determine available data points.
Furthermore, PID $20 serves a similar purpose, but for PIDs in the $21 to $3F range, and PID $40 for the $41 to $5F range. It’s worth noting that while PIDs $20 to $5F are described by SAE J1920, they may not be universally supported across all vehicles, including specific models like the BA Falcon.
For vehicles like the BA Falcon and similar models, the Mode $01 PIDs typically supported are within the initial J1979 range:
- 00: Supported PIDs $01-$20
- 01: Number of DTCs and supported/completed Mode $06 Tests
- 03: Fuel System Status
- 04: Engine Load
- 05: Engine Coolant Temperature
- 06: Short Term Fuel Trim Bank 1
- 07: Long Term Fuel Trim % Bank 1
- 08: Short Term Fuel Trim Bank 2
- 09: Long Term Fuel Trim % Bank 2
- 0a: Fuel Pressure
- 0b: Intake Manifold Pressure
- 0c: Engine RPM
- 0d: Vehicle Speed
- 0e: Timing Advance
- 0f: Intake Air Temperature
- 10: MAF Airflow
- 11: Throttle Position
- 12: Secondary Air Status
- 13: Oxygen Sensors Present (in 2 banks)
- 14: Bank 1 Sensor 1 Oxygen Sensor Voltage, Short Term Fuel Trim
- 15: Bank 1 Sensor 2 Oxygen Sensor Voltage, Short Term Fuel Trim
- 18: Bank 2 Sensor 1 Oxygen Sensor Voltage, Short Term Fuel Trim
- 19: Bank 2 Sensor 2 Oxygen Sensor Voltage, Short Term Fuel Trim
- 1c: OBD standards this vehicle conforms to
- 1d: Oxygen sensors present (in 4 banks)
When utilizing a standard OBD2 scantool that claims J1979 compliance, these are generally the parameters you can expect to retrieve from a compatible vehicle. It’s important to note that some PIDs might be excluded based on the specific vehicle’s ECU capabilities.
Regardless of the OBD2 compliant scantool you choose, these core Mode $01 J1979 PIDs will be accessible. Freeware scantool utilities often support these fundamental PID values. More advanced software may offer extended capabilities, potentially including access to EPA-mandated Mode $06 data or calculated values like 0-60mph times or virtual dyno readings based on J1979 data combined with vehicle-specific parameters.
However, for deeper diagnostics, specialized functions, or reprogramming, manufacturer-specific tools or professional-grade scan tools designed for brands like Ford are typically required. These advanced tools go beyond the standard J1979 parameters and access proprietary data and control functions.
One crucial aspect of OBD2 diagnostics is dealing with the ‘Engine Warning Light’. When this light illuminates, a Diagnostic Trouble Code (DTC) is stored in the Powertrain Control Module (PCM). J1979 compliant scantools, using Mode $03, can retrieve these DTCs. These codes are standardized and provide a textual description of the issue detected by the vehicle’s computer. Mode $04 allows for clearing these DTCs, but it is essential to address the underlying problem first to prevent the code from reappearing.
Understanding SAE J1979 and OBD2 Modes is a powerful tool for anyone working with modern vehicles. It provides a standardized way to access critical vehicle data, diagnose issues, and monitor performance, making it an indispensable part of automotive diagnostics and maintenance.
