OBD2 Engine Harness Diagrams: Your Ultimate Swap Wiring Guide

Engine swaps are a popular modification for car enthusiasts looking to boost their vehicle’s performance. For Honda Civic owners, swapping engines from different generations and models is a well-trodden path. However, navigating the wiring complexities, especially when dealing with different On-Board Diagnostics (OBD) systems, can be daunting. This guide focuses on Obd2 Engine Harness Diagrams and serves as your comprehensive resource for tackling engine swap wiring in 1992-2000 Honda Civics.

Whether you’re upgrading to a more powerful VTEC engine or swapping between OBD generations (OBD0, OBD1, and OBD2), understanding the engine harness and having access to accurate diagrams is crucial for a successful and safe swap. This article breaks down the wiring considerations for various engine and ECU combinations, providing you with the knowledge to confidently tackle your Honda engine swap project.

Understanding OBD Systems for Honda Engine Swaps

Before diving into specific wiring scenarios, it’s essential to grasp the basics of OBD systems and their relevance to engine swaps. Honda Civics from 1992 to 2000 span across three main OBD generations:

OBD0 (Pre-1992): While not directly covered in the original article focusing on 92-00 Civics, understanding OBD0 is helpful for context. OBD0 systems are simpler and less standardized than later versions. Swapping OBD0 engines into OBD1 or OBD2 vehicles requires significant wiring modifications.
OBD1 (1992-1995): OBD1 brought more standardization and diagnostic capabilities. For 92-95 Civics, OBD1 is the native system. Swapping OBD1 engines and ECUs within these models is generally more straightforward.
OBD2 (1996-2000): OBD2 is a more advanced and standardized system mandated in the US starting in 1996. 96-00 Civics utilize OBD2, which further refined diagnostics and emissions control. OBD2 systems are not directly compatible with OBD1 or OBD0 without wiring adaptations or adapter harnesses.

The complexity in engine swaps often arises when mixing OBD generations. For example, installing an OBD2 engine into an OBD1 chassis, or vice versa, necessitates careful wiring adjustments to ensure proper communication between the engine, ECU (Engine Control Unit), and the vehicle’s electrical system.

OBD1 Engine Swaps into OBD1 Civics (1992-1995)

Swapping OBD1 engines into OBD1 Civics is generally the most plug-and-play scenario. However, variations exist between different Civic models (DX, LX, CX, EX, Si, VX) and engine types (D-series, B-series).

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

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

DX/LX (D15B7): Wiring for VTEC solenoid and VTEC pressure switch is required to connect to the P28 ECU. All other connections 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 is needed for the P28 ECU (Figure 1). If your CX model has a 1-wire O2 sensor, you’ll need to wire in the additional three O2 sensor connections to the ECU as shown in Figure 1.
VX (D15Z1): VTEC wiring is required (Figure 1). For knock sensor and IAB (Intake Air Bypass) wiring, consult Figure 1. If using a chipped P28 ECU, IAB and knock sensor wiring might not be necessary. VX models with 7-wire O2 sensors will need to be converted to 4-wire O2 sensors. A diagram for 7-wire to 4-wire conversion is available at http://www.hybridautomotive.com/tech/o2/.

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

EX/Si (D16Z6): VTEC wiring is typically plug-and-play. Knock sensor and IAB wiring (Figure 1) might be needed, but often unnecessary with a chipped P28 ECU. Most other wiring is plug-and-play.
DX/LX (D15B7): VTEC, knock sensor, and IAB wiring (Figure 1) may be required. Again, chipped P28 ECUs can often bypass IAB and knock sensor wiring. Other wiring should be plug-and-play.
CX (D15B8): VTEC, knock sensor, and IAB wiring (Figure 1) are likely needed. For 1-wire O2 sensor CX models, wire in the additional O2 connections (Figure 1). Other wiring is generally plug-and-play.
VX (D15Z1): Reuse existing VTEC solenoid and pressure switch wiring for plug-and-play VTEC. 7-wire O2 sensor VX models require 7-wire to 4-wire conversion (http://www.hybridautomotive.com/tech/o2/).

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 for most components.
CX/VX (D15B8/D15Z1): Plug-and-play wiring for most components. 1-wire O2 sensor CX models need 4-wire O2 sensor wiring (Figure 1). 7-wire O2 sensor VX models need 7-wire to 4-wire conversion (http://www.hybridautomotive.com/tech/o2/).

Alt Text: OBD1 ECU wiring diagram for 92-95 Honda Civic engine swaps, detailing pin locations for VTEC, O2 sensor, knock sensor, and IAB wiring.

Alt Text: Image showing an OBD1 ECU pin removal tool being used, illustrating the process of modifying the engine harness for custom wiring.

OBD2 Engine Swaps with OBD1 ECUs into OBD1 Vehicles

This scenario involves using a newer OBD2 engine (like D16Y8, B16A2, B18C1) but retaining an OBD1 ECU (like P28, P30, P72) in an OBD1 chassis. This often requires adapter harnesses and some wiring modifications.

(Note: Again, 92 Civics with pre-run VTEC wiring benefit from using 92-95 EX/Si engine harnesses for easier VTEC connections.)

D16Y8 Swaps using P28 ECU

EX/Si/VX (D16Z6/D15Z1): Mostly plug-and-play, including VTEC. Knock sensor is not used with P28 ECU. The EX/Si/VX distributor may not directly bolt to the Y8 head; consider using the Y8 distributor with an OBD2A/OBD2B to OBD1 adapter harness. 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 might not plug in correctly. VX models may need EX/SI/DX injectors for similar flow rates. Reuse the Z6/Z1 alternator due to plug differences. The Crankshaft Position Sensor (CKF) on the Y8 is not used – secure it out of the way. VX models need 5-wire to 4-wire O2 sensor conversion (http://www.hybridautomotive.com/tech/o2/).
LX/DX/CX (D15B7/D15B8): Mostly plug-and-play. VTEC solenoid and pressure switch wiring is required (Figure 1). Reuse the DX/CX distributor or use the Y8 distributor with an OBD2A/OBD2B to OBD1 adapter harness. Relocate IAT sensor to the intake arm (Figure 3) or use a CX/DX manifold. DX injectors can be reused (same flow rate). CX models benefit from EX/SI/DX injectors for higher flow rates. Reuse the CX/DX alternator. CKF sensor on the Y8 is not used.

B16A2/B18C1 (OBD2)/B18C5 Swaps using chipped P28/P30/P72 ECUs

EX/SI/VX (D16Z6/D15Z1): Mostly plug-and-play, including VTEC. Knock sensor is not used with P28 but is used with other ECUs. Use an OBD2A/OBD2B to OBD1 adapter harness for the A2/C1/C5 distributor. Relocate IAT sensor to the intake arm. Reuse Z6 injectors. VX models need EX/SI/DX injectors. Use an OBD1 B-series alternator. CKF sensor is not used. VX models need 5-wire to 4-wire O2 conversion (http://www.hybridautomotive.com/tech/o2/).
DX/CX (D15B7/D15B8): Mostly plug-and-play. VTEC wiring is needed (Figure 1). Knock sensor is not used with P28 but is with other ECUs. Use an OBD2A/OBD2B to OBD1 adapter harness for the A2/C1/C5 distributor. Relocate IAT sensor to the intake arm. Reuse DX injectors. CX models need EX/SI/DX injectors. Use an OBD1 B-series alternator. CKF sensor is not used. 1-wire O2 sensor CX models need 4-wire conversion (Figure 1).

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

EX/SI/VX/DX/CX (D16Z6/D15Z1/D15B7/D15B8): Mostly plug-and-play. Use an OBD1 B18 distributor or an OBD2 LS distributor with an adapter harness. Use an OBD1 B-series alternator. EX/SI/DX injectors can be reused; VX/CX models need EX/DX/SI injectors. CKF sensor is not used. 1-wire O2 sensor CX models need 4-wire conversion (Figure 1). 7-wire O2 sensor VX models need 4-wire conversion (http://www.hybridautomotive.com/tech/o2/).

JDM VTEC Solenoid

Alt Text: Example of an OBD1 Intake Air Temperature (IAT) sensor relocated to the intake arm in a Honda Civic engine swap, demonstrating a common modification.

OBD0 Engine Swaps into OBD1 Vehicles using OBD1 ECUs

B18A (OBD0) Swaps using P75 OBD1 ECU
- EX/SI/DX/CX/VX (D16Z6/D15Z1/D15B7/D15B8): Mostly plug-and-play. OBD0 and OBD1 alternators use the same plugs. Reuse EX/SI/DX injectors; CX/VX models need EX/SI/DX injectors. The OBD0 fan switch is located on the back of the block, requiring rewiring from the thermostat housing. Wiring order for the fan switch doesn’t matter. 7-wire O2 sensor VX models and 1-wire O2 sensor CX models need 4-wire conversion (Figure 1 and http://www.hybridautomotive.com/tech/o2/).

Alt Text: Comparison image of OBD0 and OBD1 fan switches, highlighting the difference in connector types and locations relevant for engine swaps.

Alt Text: Image showcasing the OBD1 shock tower harness plug, which simplifies VTEC wiring in 92-95 Honda Civics when using an EX/Si harness.

OBD2 Engine Swaps into OBD2 Vehicles using OBD2 ECUs (1996-2000)

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

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). The Idle Air Control Valve (IACV) needs to be wired from 3-wire to 2-wire (Figure 6, Figure 7). The secondary O2 sensor wiring may need lengthening with an O2 adapter if using an EX catalytic converter. Relocate IAT sensor to the intake arm (Figure 8).
HX (D16Y5): Mostly plug-and-play. Reuse VTEC solenoid and pressure switch wiring. 5-speed HX models need knock sensor wiring (Figure 6, all HX models 96-00 are OBD2A wired). 7-wire O2 sensor needs 4-wire conversion (eastcoasthondas.com – eastcoasthondas Resources and Information.).

B16A2/B18C1/B18C5 Swaps using P30 (OBD2A)/P2T/P72 ECUs

EX (D16Y8): Mostly plug-and-play. Reuse VTEC solenoid, pressure switch, and knock sensor wiring. Secondary O2 sensor may need extension. B18C1 IABs need wiring to the P72 ECU (Figure 6, Figure 7). Relocate IAT sensor to the intake arm (Figure 8). B18C1/C5 can use a round style IAT and connector on the manifold (Figure 9).
DX/LX/CX (D16Y7): Mostly plug-and-play. VTEC solenoid, pressure switch, and knock sensor wiring are needed (Figure 6, Figure 7). IACV wiring from 3-wire to 2-wire (Figure 6, Figure 7). Secondary O2 sensor wiring extension may be needed. Relocate IAT sensor to the intake arm (Figure 8). B18C1/C5 can use a round style IAT and connector (Figure 9).
HX (D16Y5): Mostly plug-and-play. Reuse VTEC solenoid and pressure switch. 5-speed HX models need knock sensor wiring (Figure 6). 7-wire O2 sensor needs 4-wire conversion (eastcoasthondas.com – eastcoasthondas Resources and Information.).

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

EX/HX (D16Y8/D16Y5): Plug-and-play. HX 7-wire O2 sensor needs 4-wire conversion (eastcoasthondas.com – eastcoasthondas Resources and Information.).
DX/LX/CX (D16Y7): Mostly plug-and-play. IACV wiring from 3-wire to 2-wire (Figure 6, Figure 7). Secondary O2 sensor wiring extension may be needed. Relocate IAT sensor to the intake arm (Figure 8).

Alt Text: OBD2A hybrid pinouts diagram for 96-98 Honda Civic engine swaps, showing wiring details for VTEC, knock sensor, IACV, and O2 sensors.

Alt Text: Detailed pinout diagram for the OBD2A A-plug connector, crucial for understanding specific wire locations during engine harness modifications.

Alt Text: Image of an OBD2 pin removal tool, similar to OBD1, used for safely removing and repositioning pins in OBD2 engine harnesses during swaps.

Alt Text: OBD2B hybrid pinouts diagram for 99-01 Honda Civic engine swaps, illustrating the wiring differences compared to OBD2A systems.

Alt Text: Detailed pinout diagram for the OBD2B B-plug connector, essential for correctly wiring OBD2B engine harnesses in 99-01 Civic engine swaps.

Alt Text: Example of an OBD2 Intake Air Temperature (IAT) sensor installed in the intake arm, a necessary relocation when swapping engines into OBD2 Honda Civics.

Alt Text: Image of a round style Intake Air Temperature (IAT) sensor and connector, an alternative IAT sensor style that can be used in Honda engine swaps.

OBD1 Engine Swaps into OBD2 Vehicles using OBD1 ECUs

Swapping older OBD1 engines into newer OBD2 vehicles and using an OBD1 ECU introduces more complexity due to the need to bypass or adapt OBD2 specific sensors and systems.

D16Z6 Swaps using P28 ECU

DX/LX/CX (D16Y7): Mostly plug-and-play. VTEC solenoid and pressure switch wiring are needed (Figure 1). IACV wiring from 3-wire to 2-wire (Figure 6, Figure 7). Relocate IAT sensor to intake arm (Figure 8) or rewire IAT 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 is plug-and-play. Relocate IAT sensor (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, EGR, and secondary O2 are eliminated. 7-wire O2 sensor needs 4-wire conversion (eastcoasthondas.com – eastcoasthondas Resources and Information.). D16Z6 distributor adapter needed. Use Z6 injectors (remove clips – Figure 10). Reuse Y7 alternator.
EX (D16Y8): VTEC is plug-and-play. Relocate IAT sensor (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 (remove clips – Figure 10). Reuse Y7 alternator.

B16A2/B18C1/B18C5 Swaps using OBD1 P30 ECU

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

B18A/B Swaps using OBD1 P75 ECU

DX/LX/CX (D16Y7): Mostly plug-and-play. IACV wiring from 3-wire to 2-wire (Figure 6, Figure 7). Secondary O2 sensor wiring extension may be needed. Relocate IAT sensor (Figure 8). CKF, EVAP purge, EGR, and secondary O2 are eliminated. Use OBD2 B18B distributor or OBD2A to OBD1 distributor adapter. 99-00 Civic: OBD2B to OBD1 distributor adapter with OBD1/2 B18A/B distributor. Use B18A/B injectors (remove clips – Figure 10). Use OBD2 B-series alternator or OBD2-1 alternator adapter.
EX/HX (D16Y8/Y5): Relocate IAT sensor (Figure 8) or rewire to OBD1 style (Figure 9). CKF, EVAP purge, EGR, and secondary O2 are eliminated. 96-98 Civics: OBD2 B18B distributor or OBD2A to OBD1 distributor adapter. 99-00 Civic: OBD2B to OBD1/2 distributor adapter and OBD1/2 DOHC VTEC distributor. Use B18A/B injectors (remove clips – Figure 10). Use OBD2 B-series alternator or OBD2-1 alternator adapter. HX 7-wire O2 sensor needs 4-wire conversion (eastcoasthondas.com – eastcoasthondas Resources and Information.).

Alt Text: Image showing the modification needed for OBD2 injectors to fit OBD1 harnesses, specifically removing the injector clips for compatibility.

Alt Text: Comparison of OBD2A and OBD2B engine harnesses, emphasizing the differences in ECU connector styles that impact engine swap compatibility.

Conclusion: Wiring Success for Your Honda Engine Swap

Successfully navigating Honda engine swaps, especially across different OBD generations, hinges on understanding your engine harness and having access to reliable OBD2 engine harness diagrams. This guide provides a starting point, outlining common wiring scenarios and necessary modifications.

Remember to always consult detailed wiring diagrams specific to your engine and chassis combination. Double-check all connections before starting your engine to prevent electrical damage. When in doubt, seeking assistance from a qualified automotive electrician or Honda specialist is highly recommended. With careful planning and the right information, your Honda engine swap can be a rewarding upgrade, enhancing both performance and your understanding of automotive systems.