When modifying certain OBD1 ECUs (such as the P05), users may encounter a persistent Cruise Control indicator light when using an EX instrument cluster, or a persistent Upshift indicator light when using a CX/VX instrument cluster. This issue is caused by the ECU outputting a signal to pin D18.

Technical Overview#

The Cruise Control and Upshift indicator circuits share the same ECU output pin: D18. By tracing the circuit on the PCB, it is determined that the signal path is governed by resistor R135.

Important

Removing resistor R135 will permanently disable the signal output to pin D18, effectively turning off the indicator light on the instrument cluster.

Procedure#

1. Access the ECU: Open the ECU casing to expose the main PCB.
2. Locate R135: Identify the resistor labeled R135 on the board.
3. Removal: Desolder and remove the R135 resistor from the PCB.
4. Verification: Reassemble the ECU and verify that the indicator light no longer remains illuminated during operation.

Note

This modification is specific to OBD1 ECUs where the D18 pin is utilized for indicator light control. Ensure your specific ECU board layout matches the R135 configuration before proceeding.