What does it mean?
P1585 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cruise Control Inhibit Output Circuit Malfunction .
Symptoms
- Cruise control is permanently inhibited and cannot be engaged at all
- Alternatively the system fails to disengage cleanly when the brake or clutch is pressed, which is a safety concern
- Cruise indicator lamp does not respond to the switches
- Check engine light on with the code stored
- Engine performance under driver control remains normal
Likely causes
- Open or shorted wire in the inhibit output line between the control module and the cruise servo or relay
- Failed cruise inhibit relay, with burnt or welded contacts
- Corroded connector at the relay socket or at the servo
- Brake or clutch switch fault feeding into the inhibit logic, so the module keeps the inhibit active
- Chafed harness contacting ground or a live circuit
- Poor ground reference for the inhibit circuit
- Failed driver output inside the control module
How to fix it
- Confirm brake and clutch switch operation in live data, because a faulty input keeps the inhibit asserted
- Locate the cruise inhibit relay and swap it with an identical relay to see whether the behaviour changes
- Inspect the relay socket and the servo connector for corrosion, heat damage and loose terminals
- Measure the voltage on the inhibit output while the module is commanded to enable cruise
- Test the wiring for continuity, and for shorts to ground and to battery voltage
- Repair the harness or replace the relay first, since these are the most common failures
- Replace the control module only as a last step, then verify that cruise engages and cancels correctly on the road