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 Descriptor
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

* No Transmission Mode Switch Signal DTC P1762.
* The engine speed is greater than 500 RPM for 5 seconds.
* The system voltage is 8-18 volts.

Conditions for Setting the DTC

The Tow Mode switch remains closed, low voltage, for 600 seconds.

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 (Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
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

With a scan tool observe the Tow/Haul switch parameter in Body Controls data list. With the ignition On or engine running, operate the Tow/Haul switch several times, and observe the parameter as you operate the switch. The parameter should toggle between Active and Inactive when the switch is operated.

Circuit/System Testing

1. Ignition Off, transmission in Park, disconnect the Tow/Haul switch connector.
2. Test for less than 1 ohm of resistance between the Tow/Haul switch signal circuit terminal B and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition On, verify the scan tool Tow/Haul parameter displays Inactive.

• If not the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a fused jumper between the signal circuit and ground. Verify the scan tool parameter displays Active.

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

5. If all circuits test normal, replace the Tow/Haul switch.
6. 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).

Component Testing

Verify the Tow/Haul Mode parameter on the scan tool while cycling the tow/haul switch.

1. Ignition Off, transmission in Park, disconnect the transmission Tow/Haul switch assembly.
2. Test for infinite resistance between the Tow/Haul switch with the switch in the Open position.

• If not the specified value, replace the Tow/Haul switch assembly.

3. Depress and hold the Tow/Haul switch.
4. Test for less than 1 ohm of resistance between the Tow/Haul switch signal circuit terminals B and A while the switch is depressed.

• If greater than the specified value, replace the Tow/Haul switch assembly.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.

* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming.
* Automatic Transmission Range Selector Lever Replacement (Automatic Transmission Range Selector Lever Replacement)