6L45/6L50/6L80/6L90 - Automatic Transmission
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
* DTC P1762 is not set.
* The engine speed is greater than 400 RPM for 5 seconds.
* The ignition voltage is 8.6 volts or greater.
Conditions for Setting the DTC
The Tow/Haul Mode switch remains closed, in a low voltage condition, for 10 minutes.
Action Taken When the DTC Sets
DTC P071A is a Type C DTC.
Tow/Haul mode is inhibited.
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 6L45/6L50/6L80/6L90 - Automatic Transmission
Connector End View Reference
Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)
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 Control Module References for scan tool information
Circuit/System Verification
1. Ignition ON, cycle the Tow/Haul switch while observing the Tow/Haul switch parameter on the scan tool in the Transmission Controls Data list. The Tow/Haul switch parameter should change states from NO to YES, or YES to NO with each cycle of the switch.
• If the Tow/Haul switch parameter does not change from NO to YES or YES to NO
Refer to Circuit/System Testing below.
• If the Tow/Haul switch parameter does change from NO to YES or YES to NO
2. 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 automatic transmission shift lever electrical connector.
2. Ignition OFF, test for less than 1 ohm between terminal 2 on the automatic transmission shift lever vehicle harness connector and ground at the battery negative post.
• If 1 ohm or greater
1. Ignition OFF.
2. Test for less than 1 ohm in the ground circuit wire from both ends of the wire.
• If 1 ohm or greater, repair the open/high resistance in the wire circuit.
• If less than 1 ohm, repair the open/high resistance in the ground connection or the terminal connection at the automatic transmission shift lever.
• If less than 1 ohm
3. Ignition ON, test for greater than 11 volts on the signal circuit terminal 1 on the automatic transmission shift lever vehicle harness connector and ground at the battery negative post.
• If less than 11 volts
1. Ignition OFF.
2. Test for less than 1 ohm in the signal circuit wire from both ends of the wire.
• If 1 ohm or greater, repair the open/high resistance in the signal circuit wire.
• If less than 1 ohm, repair the open/high resistance in either terminals on the signal circuit wire.
• If greater than 11 volts
4. Ignition OFF, test for less than 3 olms between terminal 1 and terminal 2 on the automatic transmission shift lever component harness connector while depressing the Tow/Haul switch button.
• If greater than 3 ohm
Replace the automatic transmission shift lever assembly.
• If less 3 ohm
5. If all circuits test normal, replace the BCM.
Repair Instructions
* Perform the Reset Transmission Adapts Reset Procedure following all transmission related repairs.
* Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Refer to Control Module References Control Module References for Control Solenoid Valve Assembly replacement, programming, and setup.
* Automatic Transmission Range Selector Lever Replacement Service and Repair