Automatic Accord OBD2-to-OBD1 Conversion Guide
Wiring conversion guide and pinout translation tables for running an automatic OBD2a Honda Accord using an automatic OBD1 Integra ECU and separate TCU.
Unlike Honda Civics of the same era, which integrate transmission lockup controls within the ECU, automatic Honda Accords utilize a separate Transmission Control Unit (TCU).
When converting a USDM 5th-generation (1996â1997) automatic Accord from OBD2a to OBD1 for tuning (e.g., adding forced induction), standard manual-transmission OBD2-to-OBD1 jumper harnesses are insufficient because they do not route the essential TCU communication signals.
This guide outlines the components, pin mapping, and harness construction required for this conversion.
1. Required Components
To run an automatic OBD2a Accord on an OBD1 ECU and TCU, you will need:
- Automatic OBD1 P75 ECU: An automatic ECU from a 1994â1995 Integra (P75-A5x for 49-state, P75-L5x for California).
- OBD1 Accord TCU: An automatic TCU from a 1994â1995 non-VTEC Accord (F22B2 engine).
- Chipped EPROM: A ROM bin file compatible with the automatic Integra ROM and your specific engine configuration.
- Wiring Schematics: Factory service manuals for the 1994â1995 Accord (TCU), 1994â1995 Integra (ECU), and 1996 Accord (Engine harness).
Warning: This conversion requires precise electrical connections. Verify every pin against your specific factory service manuals before applying power. Incorrect wiring can damage the ECU, TCU, harness, or vehicle electronics.
2. Harness Construction Requirements
To fabricate a custom conversion harness, you will need:
- Wire: 20 AWG (general signals) and 18 AWG (power/ground lines).
- Connectors:
- OBD1 ECU Plugs: Two 26-pin, two 22-pin, and one 16-pin Tyco/AMP connectors.
- OBD2a Header: One 104-pin male pin header (sourced from a scrap OBD2a ECU or new).
- Terminals: Appropriate small and large contact pins suitable for the selected connectors.
- Tools: Standard open-barrel terminal crimping tool.
3. Pinout Translation Table (Reference)
The following table maps the 1996â1997 OBD2a Accord engine harness signals to the required OBD1 P75 ECU and OBD1 F22B2 TCU pins:
| OBD2a Accord Pin | TCU Pin | OBD1 P75 ECU Pin | Signal Name |
|---|---|---|---|
| A01 | - | A02 | Injector 4 Control |
| A02 | - | A05 | Injector 3 Control |
| A03 | - | A03 | Injector 2 Control |
| A04 | - | A01 | Injector 1 Control |
| A06 | - | A06 | Primary O2 Sensor |
(Note: Ensure all power and ground lines are cross-referenced with your specific year/model service manuals.)