Circuit/System Testing

NOTE:

This procedure will only diagnose factory installed equipment and wiring up to the X88 Tow Vehicle Electrical Receptacle.
A circuit fault or damage with the customer supplied equipment is not diagnosed or supported by GM service information.

Ignition/vehicle off, all vehicle systems OFF, disconnect the connector at the X88 Tow Vehicle Electrical Receptacle. It may take up to 2 min for all vehicle systems to power down.
Verify a test lamp illuminates between ground circuit terminal B and B+.
- If the test lamp does not illuminate.
1. Repair the open/high resistance on ground circuit or ground connection.
- Go to next step: If the test lamp illuminates.
Connect a test lamp between signal circuit terminal C and ground, ignition on/vehicle in service mode.
Verify the test lamp turns on and off when commanding the Trailer Brake Duty Cycle on and off with a scan tool.
- If the test lamp is always off.
1. Test circuit 47 for a short to ground.
  - If a short to ground is found, repair the fault on the circuit.
  - Go to next step: If a short to ground is not found.
2. Test circuit 47 for an open/high resistance.
  - If an open/high resistance is found, repair the fault on the circuit.
  - Go to next step: If an open/high resistance is not found.
3. Replace the K133 Trailer Brake Control Module.
- If the test lamp is always on.
1. Test circuit 47 for a short to voltage.
  - If a short to voltage is found, repair the fault on the circuit.
  - Go to next step: If a short to voltage is not found.
2. Replace the K133 Trailer Brake Control Module.
- Go to next step: If the test lamp turns on and off

NOTE:

The wiring of the trailer brake control circuit has been verified good to this point, recommend verifying the customers trailer brake system on the customers trailer is functioning properly before continuing.

Replace the X88 Tow Vehicle Electrical Receptacle.