Possible causes

– Weak battery- Low voltage while cranking
– Faulty Engine Control Module (ECM) relay
– Blown ECM fuse
– Faulty ECM
– ECM harness is open or shorted
– ECM circuit poor electrical connection

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)

P0688 VOLKSWAGEN Description

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