Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit/System Verification
Use the schematic to identify the following:
- Devices the vehicle is equipped with
- Device and splice pack locations on the low speed GMLAN serial data circuit
- The low speed GMLAN serial data circuit terminals for each device or splice pack
- Attempt to communicate with all devices on the low speed GMLAN serial data circuit. Refer to Data Link References .
- Verify which devices are communicating on the low speed GMLAN serial data circuit.
- If only one device is not communicating
Diagnose that device only. Refer to DTC U0100-U02FF (without HP6) , DTC U0100-U02FF (with HP6) .
- If one or more devices are communicating but not all
Refer to Circuit/System Testing - Testing the Serial Data Circuit for an Open/High Resistance .
- If none of the devices are communicating
- If only one device is not communicating
- Ignition OFF, all access doors closed, all vehicle systems OFF, all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the scan tool from the X84 Data Link Connector. The following tests will be done at the X84 Data Link Connector. It may take up to 2 minutes for all vehicle systems to power down.
- Test for less than 10 Ω between the ground circuit terminal 5 and ground.
- If 10 Ω or greater
- Ignition OFF.
- Test for less than 2 Ω in the ground circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, repair the open/high resistance in the ground connection.
- If less than 10 Ω
- Ignition ON.
- Test for less than 4.5 V between the serial data circuit terminal 1 and ground.
- If 4.5 V or greater
Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Voltage .
- If less than 4.5 V
- If 4.5 V or greater
- Ignition OFF, all access doors closed, all vehicle systems OFF, all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
- Test for greater than 100 Ω between the serial data circuit terminal 1 and ground.
- If 100 Ω or less
Refer to Circuit/System Testing - Testing the Serial Data Circuits for a Short to Ground .
- If greater than 100 Ω
- If 100 Ω or less
- Disconnect the appropriate harness connector at the first splice pack closest in the circuit to the X84 Data Link Connector.
- Test for less than 2 Ω between the X84 Data Link Connector's serial data circuit terminal 1 and the splice pack harness connector's serial data input terminal.
- If 2 Ω or greater
Repair the open/high resistance in the serial data circuit.
- If less than 2 Ω
- If 2 Ω or greater
- Replace the splice pack.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.