Possible causes

– Faulty Engine Control Module (ECM) power relay
– ECM power relay harness is open or shorted
– ECM power relay circuit poor electrical connection
– Faulty (ECM)

Tech notes

Check all the ECM fuses, if the fuses are OK try replacing the ECM relay.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0685 ACURA Description

The Engine Control Module (ECM) has detected that the ECM remains powered up after the ignition key has been turned off