P0688 AUDI Electronic Control Module Power Relay Control Circuit Open

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)