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.

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HOMESERVICE MANUALSCHEVROLET2018TAHOE FL, 4WD, GASREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISDATA COMMUNICATION SYSTEM - DIAGNOSTIC INFORMATION AND PROCEDURESDIAGNOSTIC INFORMATION AND PROCEDURESDTC U0137: LOST COMMUNICATION WITH TRAILER BRAKE CONTROL MODULECIRCUIT/SYSTEM TESTING

2018 Chevrolet Tahoe FL, 4WD, Gas

Circuit/System Testing

2018 Chevrolet Tahoe FL, 4WD, GasSECTION Circuit/System Testing

NOTE:

Use the wiring schematics and connector end views to identify the device's ground, B+, ignition, accessory wakeup serial data, and serial data circuit terminals.

Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the harness connectors at the K38A Chassis Control Module - Auxiliary. It may take up to 10 min for all vehicle systems to power down.
Test for less than 10 Ω between each ground circuit terminal and ground.
- If 10 Ω or greater
1. Ignition/Vehicle OFF.
2. 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.
- Go to next step: If less than 10 Ω
Ignition ON/Vehicle In Service Mode.
If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.
- If the test lamp does not illuminate and the circuit fuse is good
1. Ignition/Vehicle OFF, remove the test lamp.
2. Test for less than 2 Ω in the B+ circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
- If the test lamp does not illuminate and the circuit fuse is open
1. Ignition/Vehicle OFF, remove the test lamp.
2. Test for infinite resistance between the B+ circuit and ground.
  - If less than infinite resistance, repair the short to ground on the circuit.
  - If infinite resistance, replace the K38A Chassis Control Module - Auxiliary.
- Go to next step: If the test lamp illuminates
If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.
- If the test lamp does not illuminate and the circuit fuse is good
1. Ignition/Vehicle OFF, remove the test lamp.
2. Test for less than 2 Ω in the ignition circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.
- If the test lamp does not illuminate and the circuit fuse is open
1. Ignition/Vehicle OFF, remove the test lamp.
2. Test for infinite resistance between the ignition circuit and ground.
  - If less than infinite resistance, repair the short to ground on the circuit.
  - If infinite resistance, replace the K38A Chassis Control Module - Auxiliary.
- Go to next step: If the test lamp illuminates
If equipped, verify a test lamp illuminates between the accessory wakeup serial data circuit terminal and ground.
- If the test lamp does not illuminate
1. Ignition/Vehicle OFF, remove the test lamp, disconnect the harness connectors at the K9 Body Control Module and all devices that share the accessory wakeup serial data circuit.
2. Test for infinite resistance between the accessory wakeup serial data circuit and ground.
  - If less than infinite resistance, repair the short to ground on the circuit.
  - If infinite resistance
3. Test for less than 2 Ω in the accessory wakeup serial data circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If infinite resistance
4. Reconnect the K9 Body Control Module.
5. Verify a test lamp illuminates between the accessory wakeup serial data circuit terminal and ground.
  - If the test lamp does not illuminate, replace the K9 Body Control Module.
  - If the test lamp illuminates
6. Ignition/Vehicle OFF, reconnect the first device that shares the accessory wakeup serial data circuit, ignition ON/Vehicle In Service Mode.
7. Verify a test lamp illuminates between the accessory wakeup serial data circuit terminal and ground.
  - If the test lamp does not illuminate, replace the device that was just connected.
  - If the test lamp illuminates and there are more devices to connect, connect the next device and repeat step 6.7 until there are no more devices to connect.
- Go to next step: If the test lamp illuminates
Test for less than 4.5 V between each high speed GMLAN serial data circuit terminal and ground.
- If 4.5 V or greater
  Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device to test for a short to voltage.
- Go to next step: If less than 4.5 V
Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down.
Test for greater than 100 Ω between each high speed GMLAN serial data circuit terminal and ground.
- If 100 Ω or less
  Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device to test for a short to ground.
- Go to next step: If greater than 100 Ω
Disconnect the harness connectors at the K17 Electronic Brake Control Module.
Test for less than 2 Ω in each high speed GMLAN serial data circuits end to end between the K38A Chassis Control Module - Auxiliary and the K17 Electronic Brake Control Module.
- If 2 Ω or greater
  Repair the open/high resistance in the serial data circuit.
- Go to next step: If less than 2 Ω
Replace the K38A Chassis Control Module - Auxiliary.

RENDER: 1.0x

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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.