4T65-E Automatic Transaxle
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 5 separate circuits, 4 of which indicate gear selector position to the transmission control module (TCM), and 1 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 driver information center (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.
