P0078 GMC Exhaust Valve Timing Control Magnet Retarder Circuit Bank 1

Possible causes

– Faulty Exhaust Valve Timing Control Magnet Retarder
– Exhaust Valve Timing Control Magnet Retarder harness is open or shorted
– Exhaust Valve Timing Control Magnet Retarder circuit poor electrical circuit connector

What about the obd code?

An improper voltage is sent to the Engine Control Module (ECM) through exhaust valve timing control magnet retarder.

Symptoms

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

P0078 GMC Description

Exhaust valve timing control magnet retarder controls the shut/open timing of the exhaust valve by ON/OFF pulse duty signals sent from the Engine Control Module (ECM). The longer pulse width retards valve angle. The shorter pulse width advances valve angle.