P2771

DTC P2771

Diagnostic Instructions

* Perform theDiagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* ReviewStrategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC P2771
- Four Wheel Drive (4WD) Switch Circuit




Diagnostic Fault Information






Typical Scan Tool Data






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 (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Verification

1. 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.
2. 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.
3. 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

1. If any other DTCs are set, diagnose them first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions) .
2. Refer to Symptoms - Transfer Case () .
3. Replace the TCM.



Repair Instructions

Perform theDiagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.


Control Module References (Programming and Relearning) for TCM replacement, setup, and programming


Repair Verification

If another DTC is present, refer toDiagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions) and perform the appropriate diagnostic procedure.