P0851
DTC P0851
Circuit Description
The engine control module (ECM) provides 12-volts to the Park/Neutral switch of the manual shift shaft position switch. The manual shift shaft position switch is a sliding contact assembly that attaches to the manual shift shaft inside the transmission. The switch consists of five separate circuits, four of which indicate gear selector position to the transmission control module (TCM), and one that indicates Park/Neutral position to the ECM. When the transmission is in Park or Neutral, the switch closes and pulls the ECM voltage low, 0 volts. When the transmission is not in Park or Neutral, the ECM voltage is high, 12 volts. The ECM uses the switch in order to enable starter operation.
If the Park/Neutral switch and the transmission manual shift shaft position switch do not agree for a specified length of time, DTC P0851 sets. DTC P0851 is a type C DTC.
DTC Descriptor
This Diagnostic procedure supports the following DTC:
DTC P0851 Park/Neutral Position (PNP) Switch Circuit Low Voltage
Conditions for Running the DTC
* No communication DTCs U0073, U0100, U0121 or U0140.
* The ignition voltage is 9-18 volts.
* The engine is running.
Conditions for Setting the DTC
The Park/Neutral switch is open for 3.2 seconds while the TCM is reporting the gear selector is in PARK or NEUTRAL.
Action Taken When the DTC Sets
* The ECM does not illuminate the malfunction indicator lamp (MIL).
* The ECM uses the transmission range data to enable engine cranking.
* The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Failure Records.
* The ECM stores DTC P0851 in ECM history.
Conditions for Clearing the MIL/DTC
* The ECM clears the DIC message when the condition no longer exists.
* A scan tool can clear the DIC/ DTC.
* The ECM clears the DTC from ECM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.
* The ECM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the ECM.
