This harness is designed to allow tuning of OBD2B automatic transmission vehicles. Many OBD2B vehicle PCM's control the engine and the auto transmission from one unit. This dual adapter harness will split these signals so that an OBD1 ECU can be used to run the engine while the factory OBD2B PCM will handle the transmission functions. This will allow you to install any of our OBD1 AUTO ECU packages to control and tune the engine, while your factory ECU/PCM continues to control the automatic transmission.
With this harness installed, the OBD1 ECU will control the engine only. The check engine light (MIL) on the dash will illuminate if there are any trouble codes with the OBD1 ECU. You will jump the service check connector to flash codes on the light on the dash, or use the tuning system (if present) to datalog and read these codes.
With this harness installed, the factory OBD2 ECU/PCM will control the automatic transmission. The check engine light on the dash will NOT illuminate for any codes on the factory ECU/PCM. If you need to read codes from the factory OBD2 ECU/PCM, you will use an OBD2 scan tool to read through the factory OBD2 diagnostic port. The factory OBD2 ECU/PCM will always have some codes present. This is because several of the signals that would normally go to the ECU and now being redirected to the OBD1 ECU instead. This is normal, and will not affect functionality.
- 99-01 Honda CRV with automatic transmission. Overdrive is functional and works properly on this application.
- 98-02 Honda Accord 4 cylinder with automatic transmission. You must switch to a 2-wire IACV setup in order for an OBD1 ECU to run the engine properly.
- Others pending testing.
What ECU do I use?
This harness is designed to use any of our three OBD1 AUTO ECU packages:
We highly recommend that you select one of these ECU packages that your local tuning/dyno shop is familiar with. You don't want to select an ECU that your tuner is not able/willing to tune for you!
What Transmission control unit do I use?
The factory OBD2 ECU/PCM will remain in place and will control your auto transmission.
How difficult is the installation?
Installation is fairly simple. Unplug your factory OBD2 PCM and plug this harness into your factory ECU/PCM plugs. Plug in the three new OBD1 ECU connectors to your new OBD1 ECU. Plug the four remaining OBD2 ECU plugs from the new harness into your factory ECU/PCM.
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