P1778 GMC Transmission Reverse I/P Circuit Malfunction
Possible causes
– Faulty Step Motor
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
P1778 GMC Description
The step motor’s 4 aspects of ON/OFF change according to the signal from Transmission Control Module (TCM). As a result, the flow of line pressure to primary pulley is changed and pulley ratio is controlled. This diagnosis item detects when electrical system is OK, but mechanical system is NG. This diagnosis item detects when the state of the changing the speed mechanism in unit does not operate normally.
GMC Vehicle:GMC Acadia,GMC Canyon,GMC Envoy,GMC Savana 1500,GMC Savana 2500,GMC Savana 3500,GMC Sierra 1500,GMC Sierra 2500 HD,GMC Sierra 3500 HD,GMC Terrain,GMC Yukon,GMC Yukon XL 1500,GMC Yukon XL 2500,