Safety Warning

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HOMESERVICE MANUALSCHEVROLET2018SUBURBAN FL, RWD, GAS/ETHANOLREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMDATA COMMUNICATION SYSTEM - DIAGNOSTIC INFORMATION AND PROCEDURESDIAGNOSTIC INFORMATION AND PROCEDURESDTC U1026: LOST COMMUNICATION WITH TRANSFER CASE CONTROL MODULECIRCUIT/SYSTEM TESTING

2018 Chevrolet Suburban FL, RWD, Gas/Ethanol

Circuit/System Testing

2018 Chevrolet Suburban FL, RWD, Gas/EthanolSECTION 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 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 K69 Transfer Case Control Module. It may take up to 2 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 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.
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 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 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 K69 Transfer Case Control Module.
- 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 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 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 K69 Transfer Case Control Module.
- 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 OFF, remove the test lamp, disconnect the harness connectors at the K9 Body Control Module.
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 less than 2 Ω, replace the K9 Body Control Module.
- 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 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 2 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 device setting the DTC.
Test for less than 2 Ω in each serial data circuits end to end between the K69 Transfer Case Control Module and the device setting the DTC.
- 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 K69 Transfer Case Control Module.

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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.