P0688 GMC 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 description

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)