History DTC P0851 - keywords 4L60E 6L80 code M30 MIL MYC switch

This PI has been updated to remove all references to P0852 and also advise of the calibration update being available. Please discard PIP3760.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

During vehicle diagnosis DTCs P0851 may be noted as a history code in the ECM. It is possible for this DTC to set when no electrical fault exists. This condition may be caused by the Park neutral Position (PNP) switch in a 4L60E or the Internal Mode Switch (IMS) in a 6L80 reporting a different state to the ECM than to the TCM. The transmission PRNDL indicator will always display the correct transmission gear range.

A revised engine diagnostic calibration has been developed to address this issue. Reprogram the ECM with an updated software calibration. This new service calibration was released with TIS satellite data update version 4.0 or later, available April 3, 2006. As always, make sure your Tech 2® is updated with the latest software version.

After reprogramming, technicians should verify proper shifter operation and shift cable adjustment. If all shifter functions are normal, clear the DTC and restart the engine. Operate the vehicle within the "Conditions for Running the DTC" as detailed in the SI diagnostics for these DTCs while moving the shift lever through the ranges to verify that the DTC does not reset. If the DTC resets continue diagnosis using the appropriate SI diagnostics.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.