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

Symptoms

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

P0686 VOLKSWAGEN Description

The Engine Control Module (ECM) has detected a low voltage condition to the ECM.