Diagnostic Resource Only
Note: Highway 71 Auto Parts provides this guide for diagnostic purposes only. We do not sell or service this specific module. We specialize exclusively in Engine (ECM/PCM), Transmission (TCM), and Body Control Modules (BCM). If your diagnostics point to an Engine or Transmission computer failure, contact us for a programmed replacement.
Shift Motor or Computer?
Don’t fire the parts cannon. If your truck won’t shift into 4WD, follow this diagnostic path to determine if you need a new shift motor or a new control module.
The TCCM Shaking Hands Procedure
When you press the 4Hi button, the TCCM sends power to the motor and waits for the “Encoder” to tell it that the gears have moved. If the encoder stays silent, the TCCM gives up and throws a “Service 4WD” light.
👨🔧 The “Click” Test
“Turn your key to ‘Run’ but don’t start the engine. Have a friend press the 4WD buttons while you listen under the driver’s seat. If you hear a ‘Click-Click’ from the module but the motor under the truck doesn’t whir, the motor is likely seized or the wiring is cut.”
3 Steps to Confirm a Dead TCCM:
- Check for Power: Use a multimeter at the TCCM harness. No power = Blown fuse or bad ground.
- Check for Communication: If your scan tool can’t “see” the 4WD module, the module is likely dead.
- The “Fuse Pull” Reset: Pull the 4WD fuse, wait 1 minute, and reinstall. If 4WD works for one shift and then dies, the encoder is the problem. If it never works, the TCCM or Motor is dead.