Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC P0851: Park/Neutral Position (PNP) Switch Circuit Low VoltageDTC P0852: Park/Neutral Position (PNP) Switch Circuit High Voltage
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Starter Inhibit (PNP) Circuit | P0851 | P0851 | P0852 | -- |
Circuit/System Description
The transmission range (TR) switch is an integral part of the transmission control module (TCM). As the gear range selector lever is moved, the state of the Starter Inhibit Circuit may change, causing the circuit to open or close. An open circuit indicates a drive range and a low voltage signal, 0 volts, at the engine control module (ECM). A closed circuit indicates PARK or NEUTRAL and a high voltage, 12 volts, signal at the ECM.
The ECM uses the Starter Inhibit circuit status from the TCM in order to enable starter operation.
Conditions for Running the DTC
| • | Start Lock Driving voltage is within 6.0-16.0 volts. |
| • | Ignition voltage is greater than 6.5 volts. |
Conditions for Setting the DTC
P0851
The ECM detects "ON" signal from the Starter Inhibit Circuit while the TCM is commanding the Starter Inhibit Circuit "OFF" for 0.5 second.
P0852
The ECM detects "OFF" signal from the Starter Inhibit Circuit while the TCM is commanding the Starter Inhibit Circuit "ON" for 0.5 second.
Action Taken When the DTC Sets
None
Conditions for Clearing the DTC
DTC P0851 and P0852 are Type C DTCs.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics
Connector End View Reference
Scan Tool Reference
Control Module References for scan information.
DTC Type Reference
Electrical Information Reference
Circuit/System Verification
- Ignition ON, observe the DTC information with a scan tool.
- Record Freeze Frame and Failure Records.
- Clear DTCs.
- Operate the vehicle under the conditions observed in the Failure Records.
- Observe the DTC information with the scan tool. Verify that the DTC does not set.
Circuit/System Testing
- Engine ON, with the scan tool, observe the TR Sw. parameter while selecting each transmission range: P, R, N, D5, D4, D3, D2, and D1. Each selected transmission range should correspond to the correct scan tool PNP Switch parameter displayed.
- With the scan tool, observe the PNP Switch parameter (Engine Electrical/Theft Data) while selecting each transmission range: P, R, N, D5, D4, D3, D2, and D1. Each selected transmission range should correspond to the correct scan tool PNP Switch parameter displayed (Park/Neutral/In Gear).
| ⇒ | If not equal to the specified range, Test the Starter Inhibit Circuit for a short to ground, an open/high resistance, or a short to voltage. If the circuit tests normal, replace the TCM. |
| ⇒ | If not equal to the specified range, test the Starter Inhibit Circuit for a short to ground, an open/high resistance, or a short to voltage. If the circuit tests normal, replace the ECM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
