Wiring harnesses, plugs, and pin layouts vary significantly between Honda engine control unit (ECU) generations. Proper identification is critical for engine swaps, custom sensor additions (e.g., wideband controllers, EGT logging), and transmission conversions.

OBD0 Generation (1988–1991)#

OBD0 ECUs utilize three yellow harness plugs (Connectors A, B, and C).

• PR4 Layouts: For B18A1-powered vehicles, refer to the Acura Integra PR4 ECU Pinout and Schematics0 guide.
• OBD0 to OBD1 Conversion: To upgrade an OBD0 chassis to run a newer OBD1 ECU, see Kurt's OBD0-to-OBD1 Conversion Guide0.

OBD1 Generation (1992–1995)#

OBD1 ECUs use three grey plugs (A, B, and D pins) and are the most common platform for custom tuning and modifications.

Custom Wiring Modifications#

• A/C Request Switch Bypass: Instructions for triggering the A/C input line (Pin B5) on vehicles without factory air conditioning. Used to activate secondary ECU maps.
• Full-Throttle Shift Switch: Utilizing a clutch or cruise control switch to signal the ECU (Pin B8 or D10) for FTS rev-limit features.

OBD2 Generation (1996–2001)#

OBD2 layouts are divided into OBD2A (1996–1998) and OBD2B (1999–2001) configurations.

• Conversion: OBD2 ECUs are typically locked; therefore, tuners use plug-and-play conversion harnesses to adapt vehicle OBD2 plugs to an OBD1 ECU.
• Accord Conversions: For Accord-specific swap details, see the Accord OBD2-to-OBD1 Auto-to-Manual Guide0.