Circuit/System Testing

WARNING: This page is about a different car, the 2009 GMC Sierra and 2009 Chevrolet Silverado. 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.