Diagnostic Instructions
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
| • | The ignition is ON, and ignition voltage is greater than 9 V and less than 18 V. |
| • | The engine speed is greater than 200 RPM and less than 7500 RPM for 5 seconds. |
Conditions for Setting the DTC
The Tow/Haul Mode switch remains closed for greater than 20 seconds.
Action Taken When the DTC Sets
Tow/Haul mode is disabled.
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.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
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, cycle the tow/haul switch while observing the Tow/Haul Mode parameter on the scan tool. The Tow/Haul Mode parameter should change states between Active and Inactive with each cycle of the switch.
- Operate the vehicle within the Conditions for Running the DTC to verify that the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Circuit/System Testing
- Ignition OFF, disconnect the automatic transmission shift lever harness connector.
- Test for less than 5 ohms between the ground circuit terminal B and ground.
| ⇒ | If greater than the specified value, test the ground circuit for an open/high resistance. |
- Ignition ON, test for greater than 11 V between the ignition voltage circuit terminal A and ground.
| ⇒ | If less than the specified value, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
- Verify less than 1 ohm between terminal A and terminal B of the automatic transmission shift lever, while pressing the tow/haul switch button.
| ⇒ | If greater than the specified value, replace the automatic transmission shift lever. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
