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)

P0688 Information for specific makes

P0688 AUDI
P0688 CHRYSLER
P0688 DODGE
P0688 JEEP
P0688 MITSUBISHI
P0688 VOLKSWAGEN