Information on False DTC P0850 Park/Neutral Position (PNP) Switch Circuit Code Found in Transmission Control Module (TCM) History (08-07-30-038)

Publication date: 2008-08-19
Reference number: 08-07-30-038

Information on False DTC P0850 Park/Neutral Position (PNP) Switch Circuit Code Found in Transmission Control Module (TCM) History

TECHNICAL SERVICE BULLETIN

Reference Number(s): 08-07-30-038, Date of Issue: August 19, 2008

Affected Model(s):

2008-2009 Pontiac G8

SERVICE INFORMATION

The current operating software and calibration may result in the setting of a false history diagnostic trouble code (DTC) P0850 (Park/Neutral Position (PNP) Switch Circuit) in some automatic transmissions.

The Park/Neutral switch signal is compared to the transmission range position switches (inside the transmission) to determine if the switch signal is plausible. If they do not agree after an elapsed time, the transmission selector is assumed to be correct and DTC P0850 is set. The ECM then uses the transmission range data to enable engine cranking.

The conditions for setting DTC P0850 are as follows:

The park/neutral switch circuit is low, 0 volts, for 100 seconds while the TCM is reporting the gear selector is in REVERSE or any forward range.
The park/neutral switch circuit is high, 12 volts, for 200 seconds while the TCM is reporting the gear selector is in PARK or NEUTRAL.

IMPORTANT: DTC P0850 will not illuminate the Malfunction Indicator Lamp (MIL).

If a customer brings in a vehicle for service with the Malfunction Indicator Lamp (MIL) on, check and diagnose alternative DTCs first. DO NOT diagnose history code P0850.

To avoid misdiagnosis and encourage "Fix It Right the First Time", diagnose the condition that set the MIL.

If an actual Park/Neutral switch is found to be faulty, there will be subsequent DTCs that will set and illuminate the MIL.