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 Descriptor
DTC P2771: Four Wheel Drive (4WD) Switch CircuitDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Operating Conditions: Ignition ON, engine OFF, transfer case shift control switch in 2 HI. | ||||
4 WD Low Indicator Light Parameter | 0 V | 0 V | 0 V | -- |
Typical Scan Tool Data
Display Parameters | Normal Range | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|---|
Operating Conditions: Engine running, cycle through ranges | ||||
4 WD Low Indicator Light Parameter | Off | On | Off | Off |
Circuit/System Description
On vehicles equipped with 4 wheel drive, the output speed sensor is on the transfer case. The instrument panel mounted transfer case shift control switch consist of a 2HI position, 4HI and 4 Low. The transfer case shift control module continuously monitors the signal to determine the position selected by the vehicle operator. The transfer case shift control module communicates the status of the transfer case shift control switch to the transmission control module (TCM). When the switch is in the 4 Low position, the TCM multiples the transfer case output shaft speed by the transfer case ratio in 4 Low to determine the transmission output shaft speed. The TCM uses this information to provide earlier upshifts and also to prevent an overspeed condition in 4 Low.
Conditions for Running the DTC
| • | Engine running for greater than 5 seconds. |
| • | Output speed greater than 60 RPM. |
| • | Transmission fluid temperature between 20°C (68°F) and 130°C (266°F). |
| • | Shift is complete and range attained is not neutral. |
| • | DTCs P0721 and/or P0722 are not active. |
Conditions for Setting the DTC
Condition 1
Transfer case four wheel drive switch indicates high range and the calculated transfer case range is low for 5 seconds.
Condition 2
Transfer case four wheel drive switch indicates low range and the calculated transfer case range is high for 5 seconds.
Action Taken When the DTC Sets
| • | The TCM detects four wheel drive high and low range with calculated speed ratios. |
| • | The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL) on the second consecutive occurrence. |
| • | DTC P2771 is stored in TCM history. |
Conditions for Clearing the DTC
DTC P2771 is a Type B DTC.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics
Connector End View Reference
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, place the transfer case shift control switch in the 2 HI position. Verify the 2 high indicator light on the switch is ON and not flashing.
- Ignition ON, transmission in Neutral, observe the scan tool 4WD Low parameter. The parameter should change from Disabled, to Enabled when selecting the 4 Low position and the 4WD low indicator light is ON and not flashing.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
- If any other DTCs are set, diagnose them first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.
- Refer to Symptoms - Transfer Case.
- Replace the TCM.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for TCM replacement, setup, and programming
Repair Verification
If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
