What does it mean?
U1026 is a Network (CAN bus, module communications) fault code. It indicates: No Communication With Transfer Case Shift Control Module .
Symptoms
- Four wheel drive or low range cannot be selected, or the selection is ignored
- Service four wheel drive message or warning lamp on the dash
- Transfer case stuck in the last selected mode
- Mode selector switch lights flashing or all off
- Scan tool cannot communicate with the transfer case module while other modules answer
- Possible driveline binding if the system is stuck in an engaged mode
Likely causes
- Blown fuse or failed relay supplying the transfer case control module
- Corroded or water damaged module connector, since the unit is often mounted low or under the vehicle
- Open or intermittent bus wiring between the transfer case module and the gateway
- Poor ground at the transfer case module mounting point
- Internal module failure, including a burnt motor driver circuit
- Harness damage from road debris, undertray contact or corrosion along the chassis rail
- Low system voltage keeping the module from powering up correctly
How to fix it
- Attempt to communicate with the transfer case module and note which other modules on the same bus still respond
- Check the fuses and relays that supply the module before testing any wiring
- Locate the module, inspect its connector for water, corrosion and damaged seals, then reseat it
- Measure power and ground at the module with the ignition on and do a voltage drop test on the ground
- Follow the harness along the chassis and undertray, looking for road damage, chafing and corroded splices
- Test the bus lines for continuity, shorts to ground and shorts to battery voltage between the module and the gateway
- Check the transfer case motor and encoder circuits for shorts that could have damaged the module
- Replace and program the transfer case control module only after supply, ground and bus wiring are proven good