Circuit/System Testing

WARNING: This page is about a different car, the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Disconnect the transmission 20-way connector and observe the Park/Neutral scan tool parameter in the engine controls data list. The parameter should display In-Gear.

If the Park/Neutral parameter does not display In-Gear test the Park/Neutral signal circuit between the engine side of the transmission 20-way connector and the ECM connector for a short to ground.

If the Park/Neutral parameter displays In-Gear test the transmission IMS for a shorted P/N circuit to ground. Inspect the harness for damage or chaffing.

If the IMS was not shorted to ground, test the IMS Park/Neutral signal circuit form the IMS connector on the TCM side of the 20-way connector for an open or short to ground.

If no concerns are found, replace the ECM. Refer to Control Module References for replacement, setup, and programming.