P071A

DTC P071A

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.

DTC Descriptors
DTC P071A
- Transmission Tow Mode Switch Circuit

Circuit/System Description

Tow/haul mode enables the operator to achieve enhanced shift performance when towing or hauling a load. When tow/haul mode is selected, the tow/haul switch input signal to the body control module (BCM) is momentarily toggled to zero volts. This signals the transmission control module (TCM) to extend the length of time between upshifts and increase transmission line pressure. Cycling the tow/haul switch again disables tow/haul mode and returns the transmission to a normal shift pattern.

Conditions for Running the DTC

* DTC P1762 is not set.
* The engine speed is 400 RPM or greater for 5 seconds.
* The ignition voltage is 8.6 volts or greater.

Conditions for Setting the DTC

The Tow Mode switch signal circuit has low voltage for 10 minutes.

Action Taken When the DTC Sets

DTC P071A is a type C DTC.

Conditions for Clearing the DTC

DTC P071A is a type C DTC.

Diagnostic Aids

If the electrical circuit tests are OK and the shift pattern is not occurring, there may be a mechanical/hydraulic condition that prevents operation. Refer to Symptoms - Automatic Transmission (Symptoms - Automatic Transmission).

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference

* Component Connector End Views (Connector End Views By Name)
* Inline Harness Connector End Views (Connector End Views By Number)

Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Description and Operation

Electronic Component Description (Electronic Component Description)
DTC Type Reference

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

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

Circuit/System Verification

1. Ignition ON, engine OFF, observe the Tow/Haul parameter with a scan tool. Operate the Tow/Haul switch several times. The Tow/Haul parameter should toggle between Active and Inactive when the switch is operated.
2. If the electrical circuit checks are OK and the tow/haul shift pattern is not occurring, there may be a mechanical/hydraulic condition that prevents tow/haul operation. Refer to Symptoms - Automatic Transmission (Symptoms - Automatic Transmission).
3. After performing the above steps, verify that the DTC does not reset by operating the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions you observe from the Freeze Frame/Failure Records data. If the vehicle passes the Circuit/System Verification procedure, then STOP. Do not perform the Circuit/System Testing or Component Testing as this may result in an unnecessary part replacement. Refer to Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections).

Circuit/System Testing

1. Ignition OFF, transmission in Park, disconnect the I/P Multifunction Switch connector.
2. Install a 3 amp fused jumper between the Tow/Haul Switch signal circuit harness connector terminal 11 and ground. Verify the scan tool parameter changes between Active and Inactive each time the signal circuit is grounded.

• If not the specified value, test the signal circuit for a short to voltage, short to ground, or an open/high resistance. If the circuit tests normal, replace the BCM.

3. If all circuits test normal, replace the Tow/Haul switch.

Repair Instructions

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

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