Diagnostic Aids

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Disconnecting the 16-way connector from the transmission will disable TCM and ECM communications.
A loose or unlocked transmission 16-way connector can cause DTC P0852 to set as well as a no start condition.
If the engine will not start, look for an open in the PNP signal circuit.
- If an open is found, go to Circuit/System Testing .
The IMS is part of a 6 wire harness, which connects electrically to the control solenoid (w/body and TCM) valve assembly. Inspect the IMS, harness, connector, and control solenoid (w/body and TCM) valve assembly electrical pins for metallic debris. Use a terminal test kit for any test that requires probing the control solenoid (w/body and TCM) valve assembly harness connector or a component harness connector.
Use the scan tool IMS parameters to compare them to the ECM P/N parameter. When the transmission is in park or neutral, the ECM P/N switch parameter will read park/neutral. When the transmission is in a drive range, the P/N will read In Gear. Be alert for scan tool data parameters which frequently toggle or vary while testing. Switch positions which are transitional, display invalid or are open are not normal IMS positions when shifter detents are engaged.
With the engine running, compare the PNP switch state to the range selector positions. Move the shifter through all gear ranges. If the PNP switch parameter always reads Park/Neutral in all positions, test the signal circuit from the ECM to the transmission for a short to ground.
- If a short is not found, go to Component Testing to evaluate the manual shift shaft switch assembly and the control solenoid (w/body and TCM) valve assembly.
  Due to the properties of the stainless steel contact strips inside the switch, it is difficult to obtain meaningful resistance readings. For this reason, measuring the switch resistance may not help to conclude a faulty switch. However, the absence of all resistance where there should be would indicate a circuit failure.
If the PNP switch parameter always reads In Gear in all gear ranges, test the signal circuit pin 3 of the transmission 16-way connector to pin F of the control solenoid (w/body and TCM) valve assembly side for an open.
- If no open is found, replace the manual shift shaft switch assembly.
Note - In order to view the Park/Neutral data parameters with the engine off, it may be necessary to place the transmission shifter in gear and then move the start switch to the start position. This will allow the parameter to operate without the engine running.