Honda OBD2 Plugs and Wires: Your Comprehensive Guide to Engine Swap Wiring

Engine swaps in Honda vehicles, especially models from the 90s and early 2000s, are a popular modification for enthusiasts looking to boost performance or replace aging engines. A crucial aspect of any successful Honda engine swap is understanding and correctly wiring the OBD (On-Board Diagnostics) system. Specifically, knowing about Honda Obd2 Plugs And Wires is paramount when dealing with newer engines or ECUs (Engine Control Units) in older Honda chassis.

This guide aims to be your ultimate resource for navigating the complexities of Honda engine swap wiring, focusing on OBD2 systems and ensuring a smooth integration. Whether you’re swapping a VTEC or non-VTEC engine, dealing with OBD1 or OBD2 ECUs, or converting between OBD generations, this article will provide the essential information you need.

Understanding OBD Systems in Honda Vehicles

Before diving into specific wiring scenarios, it’s important to grasp the basics of Honda’s OBD systems. OBD is a standardized system used in vehicles to monitor emissions and engine performance. Honda vehicles, particularly Civics, have transitioned through different OBD generations:

• OBD0 (Pre-1992): Early diagnostic systems, less standardized and not heavily reliant on plugs and standardized wiring like later systems.
• OBD1 (1992-1995): Introduced more standardized connectors and diagnostic capabilities. Found in 92-95 Civics and Integras.
• OBD2 (1996-2000/2001+): Further standardization, enhanced diagnostic features, and different connector types (OBD2A and OBD2B). 96-00 Civics are predominantly OBD2.

The key challenge in engine swaps often arises when mixing and matching engines and chassis with different OBD generations. This is where understanding Honda OBD2 plugs and wires becomes critical, as you’ll likely need to adapt wiring harnesses, relocate sensors, or even use adapter harnesses to ensure compatibility.

OBD1 Engine/ECU Swaps into OBD1 Civic (1992-1995)

If you’re keeping it simple and swapping an OBD1 engine into an OBD1 Civic, the process is generally more straightforward. However, depending on your original Civic model (DX, LX, CX, EX, Si, VX) and the engine you’re swapping in, some wiring adjustments may still be necessary, particularly for VTEC engagement and additional sensors.

(Note: For all 92 Civics, the VTEC wiring is pre-run on the shock tower to ECU harness. Using a 92-95 EX/Si engine harness simplifies VTEC wiring.)

1. D16Z6/D15B (JDM)/Mini-Me Swaps using P28 ECU

• DX/LX (D15B7): You’ll need to wire the VTEC solenoid and VTEC pressure switch to the P28 ECU. The rest should be plug-and-play. Refer to Figure 1 for OBD1 ECU wiring details.
• CX (D15B8): Similar to DX/LX, VTEC solenoid and pressure switch wiring are needed (Figure 1). If your CX is not a 4-wire O2 sensor model, you’ll also need to wire the three additional O2 sensor connections to the ECU (Figure 1).
• VX (D15Z1): VTEC wiring as above. For knock sensor and IAB (Intake Air Bypass) wiring, see Figure 1. If using a chipped P28 ECU, IAB and knock sensor wiring may not be necessary. VX models with 7-wire O2 sensors will need conversion to 4-wire O2 sensors. Consult http://www.hybridautomotive.com/tech/o2/ for a 7-wire to 4-wire O2 conversion diagram.

2. B16A3/B17A/B18C1/B18C (OBD1 JDM) Swaps using Chipped P28/P30/P61/P72 ECU

• EX/Si (D16Z6): VTEC is typically plug-and-play. Knock sensor and IAB wiring might be needed (Figure 1), but often bypassed with chipped ECUs.
• DX/LX (D15B7): VTEC, knock sensor, and IAB wiring as per Figure 1. Again, chipped P28 ECUs can negate the need for IAB and knock sensor wiring.
• CX (D15B8): VTEC, knock sensor, and IAB wiring (Figure 1). 4-wire O2 sensor wiring might be needed for non-4-wire CX models.
• VX (D15Z1): Reuse existing VTEC wiring. 7-wire to 4-wire O2 conversion may be required.

3. B18A (OBD1)/B18B Swaps in DX/CX/VX/EX using P74/P75 ECU or Chipped OBD1 ECUs

• LX/DX/EX (D15B7/D16Z6): Plug-and-play wiring in most cases.
• CX/VX (D15B8/D15Z1): Mostly plug-and-play. 4-wire O2 sensor wiring for 1-wire CX models. 7-wire to 4-wire O2 conversion for VX models.

Figure 1: OBD1 ECU Wiring Diagram and Pin Removal

Alt text: OBD1 ECU wiring diagram for 92-95 Honda Civic engine swaps, detailing pinouts for common modifications like VTEC and O2 sensor wiring, crucial for understanding Honda OBD2 plugs and wires compatibility.

Alt text: Image showing an OBD1 ECU pin removal tool, essential for safely modifying Honda OBD2 plugs and wires during engine swap wiring processes.

Figure 2: JDM D15B VTEC Pressure Switch

JDM D15B VTEC Solenoid Bolt

Alt text: Location of the VTEC pressure switch bolt on a JDM D15B engine, highlighting a potential area requiring attention when dealing with Honda OBD2 plugs and wires related to VTEC system.

(Note: If your JDM D15B engine lacks a VTEC pressure switch, you’ll need to install one from any 90-01 Civic/Integra/Accord. Simply unscrew the bolt shown in Figure 2 and thread in the pressure switch.)

OBD2 Engine/OBD1 ECU Swaps into OBD1 Vehicle (1992-1995)

Swapping an OBD2 engine into an OBD1 chassis requires more wiring adaptations to make the newer engine communicate with the older OBD1 ECU. This often involves sensor relocation and understanding the differences in Honda OBD2 plugs and wires compared to OBD1.

(Note: VTEC wiring remains plug-and-play for 92 Civics with 92-95 EX/Si engine harnesses.)

1. D16Y8 Swaps using P28 ECU

• EX/Si/VX (D16Z6/D15Z1): Mostly plug-and-play for basic engine functions and VTEC. The knock sensor will not be used with the P28 ECU. The EX/Si/VX distributor may not directly bolt onto the Y8 head. You can use it, but not all mounting points will align. To use the Y8 distributor, an OBD2A or OBD2B to OBD1 adapter harness is needed. Relocate the intake air temperature (IAT) sensor to the intake arm (Figure 3) or use a Z6/Z1 intake manifold. Reuse Z6 injectors as Y8 injectors may not plug in correctly. For VX models, consider EX/SI/DX injectors for similar flow rates. Reuse the Z6/Z1 alternator due to plug style differences. The crankshaft fluctuation sensor (CKF) on the Y8 will not be used – secure it out of the way. For VX models, 5-wire O2 to 4-wire conversion is needed (refer to http://www.hybridautomotive.com/tech/o2/).
• LX/DX/CX (D15B7/D15B8): Mostly plug-and-play. VTEC solenoid and pressure switch wiring are required (Figure 1). Reuse the DX/CX distributor. For Y8 distributor use, OBD2A/B to OBD1 adapter is needed. Relocate IAT sensor to the intake arm (Figure 3) or use a CX/DX manifold. DX injectors can be reused as flow rates are similar. For CX models, consider EX/SI/DX injectors for better flow. Reuse the CX/DX alternator. CKF sensor on Y8 is not used.

2. B16A2/B18C1 (OBD2)/B18C5 Swaps using Chipped P28/P30/P72 ECU

• EX/SI/VX (D16Z6/D15Z1): Mostly plug-and-play, VTEC plug-and-play. Knock sensor is not used with P28 ECU but will be with others. OBD2A/B to OBD1 adapter harness needed for A2/C1/C5 distributor. Relocate IAT sensor to the intake arm. Reuse Z6 injectors. For VX, use EX/SI/DX injectors. Use an OBD1 B-series alternator. CKF sensor not used. 5-wire to 4-wire O2 conversion for VX.
• DX/CX (D15B7/D15B8): Mostly plug-and-play. VTEC wiring needed (Figure 1). Knock sensor not used with P28 but with others. OBD2A/B to OBD1 adapter harness for A2/C1/C5 distributor. IAT sensor relocation to intake arm. Reuse DX injectors. For CX, use EX/SI/DX injectors. OBD1 B-series alternator needed. CKF sensor not used. 1-wire to 4-wire O2 conversion for CX.

3. B18B/B20B/Z (OBD2) Swaps using P75 ECU

• EX/SI/VX/DX/CX (D16Z6/D15Z1/D15B7/D15B8): Mostly plug-and-play. Use OBD1 B18 distributor or OBD2 LS distributor with adapter harness. OBD1 B-series alternator needed. For EX/SI/DX, reuse EX/SI/DX injectors; for VX/CX, use EX/DX/SI injectors. CKF sensor not used. 1-wire to 4-wire O2 for CX and 7-wire to 4-wire O2 for VX.

Figure 3: OBD1 IAT Sensor in Intake Arm

Alt text: Example of an OBD1 IAT sensor relocated to the intake arm during a Honda engine swap, a common modification when dealing with Honda OBD2 plugs and wires in conversions.

OBD0 Engine Swaps into OBD1 Vehicle using OBD1 ECU

Swapping an older OBD0 engine into an OBD1 Civic is generally quite plug-and-play for the main engine harness. The primary wiring modification typically involves the cooling fan switch location.

1. B18A (OBD0) Swaps using P75 OBD1 ECU

• EX/SI/DX/CX/VX (D16Z6/D15Z1/D15B7/D15B8): Mostly plug-and-play. OBD0 and OBD1 alternator plugs are compatible. Reuse EX/SI/DX injectors; for CX/VX, use EX/SI/DX injectors. The fan switch location is different on OBD0 engines (back of the block). Rewire the fan switch from the thermostat housing to the back of the block. Wiring order for the fan switch doesn’t matter. For VX (7-wire O2) and CX (1-wire O2), use Figure 1 for 4-wire O2 conversion.

Figure 4: OBD0 vs. OBD1 Fan Switch Locations

Alt text: Comparison of OBD0 and OBD1 fan switch locations on Honda engines, illustrating a necessary wiring adjustment when working with Honda OBD2 plugs and wires in older engine swaps.

Figure 5: OBD1 Shock Tower Harness Plug

Alt text: Image of an OBD1 shock tower harness plug in a Honda Civic, showcasing a key connection point in the engine wiring system relevant to Honda OBD2 plugs and wires and engine swap compatibility.

OBD2 Engine Swaps into OBD2 Vehicle using OBD2 ECU (1996-2000 Civic)

(Important Note: 96-98 OBD2A and 99-00 OBD2B engine and dash harnesses are NOT interchangeable due to different ECU connectors – see Figure 11.)

1. D16Y8 Swaps using P2P ECU

• DX/LX/CX (D16Y7): Mostly plug-and-play. VTEC solenoid, VTEC pressure switch, and knock sensor wiring are needed (Figure 6 for OBD2A, Figure 7 for OBD2B). Idle air control valve (IACV) wiring from 3-wire to 2-wire is also required (Figure 6 & 7). Lengthen secondary O2 sensor wiring if using an EX-style catalytic converter. Relocate IAT sensor to the intake arm (Figure 8).
• HX (D16Y5): Mostly plug-and-play. Reuse VTEC solenoid and pressure switch. 5-speed models need knock sensor wiring (CVT models already have knock sensor wiring) (Figure 6 – HX models are OBD2A). 7-wire O2 to 4-wire conversion needed (eastcoasthondas.com – eastcoasthondas Resources and Information.).

2. B16A2/B18C1/B18C5 Swaps using P30 (OBD2A)/P2T/P72 ECU

• EX (D16Y8): Mostly plug-and-play. Reuse VTEC, pressure switch, and knock sensor wiring. Secondary O2 extension might be needed. For B18C1, IAB wiring is required for P72 ECU (Figure 6 & 7). IAT sensor relocation to the intake arm. For B18C1/C5, consider converting to a round-style IAT with a connector on the manifold (Figure 9).
• DX/LX/CX (D16Y7): Mostly plug-and-play. VTEC, pressure switch, and knock sensor wiring needed (Figure 6 & 7). IACV 3-wire to 2-wire conversion (Figure 6 & 7). Secondary O2 extension. IAT sensor relocation (Figure 8). Round-style IAT conversion for B18C1/C5 (Figure 9).
• HX (D16Y5): Mostly plug-and-play. Reuse VTEC and pressure switch. 5-speed HX models need knock sensor wiring (Figure 6). 7-wire O2 to 4-wire conversion.

3. B18B/B20B/Z Swaps using OBD2A P75 ECU (Avoid 00-01 P75 due to immobilizer)

• EX/HX (D16Y8/D16Y5): Plug-and-play. 7-wire to 4-wire O2 for HX.
• DX/LX/CX (D16Y7): Mostly plug-and-play. IACV 3-wire to 2-wire conversion (Figure 6 & 7). Secondary O2 extension. IAT sensor relocation (Figure 8).

Figure 6: OBD2A Hybrid Pinouts (1996-1998)

Alt text: OBD2A ECU wiring diagram for 96-98 Honda Civic engine swaps, illustrating pin assignments for hybrid conversions and highlighting the role of Honda OBD2 plugs and wires in these systems.

Alt text: Detailed OBD2A A plug pinout diagram, crucial for understanding specific wire connections within Honda OBD2 plugs and wires during engine swaps in 96-98 Civics.

Alt text: Image of an OBD2 pin removal tool, necessary for modifying and working with Honda OBD2 plugs and wires in 96-00 Honda Civic engine swaps.

Figure 7: OBD2B Hybrid Pinouts (1999-2000/2001)

Alt text: OBD2B ECU wiring diagram for 99-00/01 Honda Civic engine swaps, showcasing wiring configurations relevant to Honda OBD2 plugs and wires in later OBD2 systems.

Alt text: Detailed OBD2B B plug pinout diagram, essential for precise wiring modifications involving Honda OBD2 plugs and wires in 99-00/01 Honda Civic engine swaps.

Figure 8: OBD2 IAT Sensor in Intake Arm

Alt text: Example of an OBD2 IAT sensor relocated to the intake arm in a Honda engine swap, a common adjustment due to manifold differences and relevant to Honda OBD2 plugs and wires modifications.

Figure 9: Round Style IAT Sensor

Alt text: Image of a round style IAT sensor and its connector, showing an alternative IAT sensor type that can be used in Honda engine swaps involving Honda OBD2 plugs and wires.

OBD1 Engine Swaps into OBD2 Vehicle using OBD1 ECU (1996-2000 Civic)

This is a common scenario for those wanting to use older, more tunable OBD1 ECUs in newer OBD2 Civics. It requires significant wiring modifications and understanding the differences in sensor compatibility and Honda OBD2 plugs and wires.

1. D16Z6 Swaps using P28 ECU

• DX/LX/CX (D16Y7): Mostly plug-and-play for basic engine operation. VTEC solenoid and pressure switch wiring are needed (Figure 1). IACV 3-wire to 2-wire conversion (Figure 6 & 7). IAT sensor relocation to intake arm (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, and secondary O2 are eliminated. D16Z6 distributor needs an adapter. Use Z6 injectors and remove injector “clips” for plug-and-play (Figure 10). Reuse Y7 alternator.
• HX (D16Y5): VTEC plug-and-play. IAT sensor relocation (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, EGR, and secondary O2 are eliminated. 7-wire O2 to 4-wire conversion. D16Z6 distributor adapter needed. Use Z6 injectors and remove “clips” (Figure 10). Reuse Y7 alternator.
• EX (D16Y8): VTEC plug-and-play. IAT sensor relocation (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, EGR, and secondary O2 are eliminated. D16Z6 distributor adapter needed. Use Z6 injectors and remove “clips” (Figure 10). Reuse Y7 alternator.

2. B16A2/B18C1/B18C5 Swaps using OBD1 P30 ECU

• DX/LX/CX (D16Y7): Mostly plug-and-play. VTEC solenoid, pressure switch, and knock sensor wiring needed (Figure 1). IACV 3-wire to 2-wire (Figure 6 & 7). IAT sensor relocation (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, and secondary O2 eliminated. For 96-98 Civics, use an OBD2 B-series VTEC distributor or OBD2A to OBD1 distributor adapter. For 99-00, use OBD2B to OBD1/2 distributor adapter and OBD1/2 B-series DOHC VTEC distributor. Use B-series injectors and remove “clips” (Figure 10). Use OBD2 B-series alternator.
• HX (D16Y5): VTEC plug-and-play. IAT sensor relocation (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, EGR, and secondary O2 eliminated. 7-wire O2 to 4-wire conversion. Use OBD2 VTEC distributor or OBD2A to OBD1 distributor adapter. Use B-series injectors and remove “clips” (Figure 10). Use OBD2 B-series alternator.
• EX (D16Y8): VTEC plug-and-play. Knock sensor wiring needed (Figure 1). IAT sensor relocation (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, EGR, and secondary O2 eliminated. For 96-98 Civics, use OBD2 B-series VTEC distributor or OBD2A to OBD1 distributor adapter. For 99-00, use OBD2B to OBD1/2 distributor adapter and OBD1/2 B-series DOHC VTEC distributor. Use B-series injectors and remove “clips” (Figure 10) or use Y8 injectors. Use OBD2 B-series alternator.

3. B18A/B Swaps using OBD1 P75 ECU

• DX/LX/CX (D16Y7): Mostly plug-and-play. IACV 3-wire to 2-wire (Figure 6 & 7). Secondary O2 extension (if using EX cat). IAT sensor relocation (Figure 8). CKF, EVAP purge, EGR, and secondary O2 eliminated. Use OBD2 B18B distributor or OBD2A to OBD1 distributor adapter. For 99-00 Civic, use OBD2B to OBD1 distributor adapter with OBD1 or OBD2 B18A/B distributor. Use B18A/B injectors and remove “clips” (Figure 10). Use OBD2 B-series alternator.
• EX/HX (D16Y8/Y5): IAT sensor relocation (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, EGR, and secondary O2 eliminated. For 96-98 Civics, use OBD2 B18B distributor or OBD2A to OBD1 distributor adapter. For 99-00, use OBD2B to OBD1/2 distributor adapter and OBD1/2 B-series DOHC VTEC distributor. Use B18A/B injectors and remove “clips” (Figure 10). Use OBD2 B-series alternator. 7-wire to 4-wire O2 for HX.

Figure 10: OBD2 to OBD1 Injector Clip Modification

Alt text: Image illustrating the modification needed for OBD2 injector clips to fit OBD1 injector plugs, a common wiring adjustment when dealing with Honda OBD2 plugs and wires in engine swaps.

Figure 11: OBD2A vs. OBD2B Harness Comparison

Alt text: Visual comparison of OBD2A and OBD2B wiring harnesses, highlighting the differences in ECU connectors and wiring layouts that are critical to understand when working with Honda OBD2 plugs and wires in 96-00 Civic engine swaps.

Conclusion: Mastering Honda OBD2 Plugs and Wires for Successful Engine Swaps

Successfully navigating Honda engine swaps, especially when dealing with different OBD generations, hinges on a solid understanding of Honda OBD2 plugs and wires. This guide provides a detailed overview of common swap scenarios and the necessary wiring modifications. By carefully identifying your engine and chassis combinations, consulting the provided figures and diagrams, and paying close attention to sensor compatibility and ECU requirements, you can confidently tackle your Honda engine swap wiring. Remember to always double-check your connections and consult professional resources if you encounter any uncertainties during your wiring process. Proper wiring is not just about getting your engine to run; it’s about ensuring the longevity, reliability, and optimal performance of your Honda swap project.