What does it mean?
U1107 is a Network (CAN bus, module communications) fault code. It indicates: ECU In Single-Wire Mode .
Symptoms
- Warning lamps illuminate and several systems report faults at the same time
- Communication is unstable, with modules appearing and disappearing on the scan tool
- The fault often appears on rough roads, over bumps or after vibration
- Convenience or driver assistance functions become unavailable
- Codes return shortly after being cleared
- Slow response from gauges and driver information displays
Likely causes
- Open circuit in the CAN high or CAN low wire, often where the harness flexes or passes through a grommet
- Short to ground or short to battery on one of the two bus wires
- Chafed insulation where the harness rubs a bracket, engine mount or body panel
- Corroded or loose terminal in a bus connector, letting one line drop out intermittently
- A module with an internal fault pulling one line out of range
- Poor repair work, such as an untwisted or badly joined section of the CAN pair
- Missing or damaged terminating resistor
How to fix it
- Back-probe the CAN high and CAN low wires with the ignition on and compare them; the faulty line will sit at ground, at battery voltage or float instead of near its normal resting level
- Check resistance across the pair with power removed to confirm the terminating resistors
- Wiggle test the harness at grommets, hinge points and along the frame while watching the meter or the scan data
- Inspect connectors for green corrosion, moisture and pushed-back terminals, and repair with properly crimped, sealed joints
- Trace the failed line end to end for chafe points against metal brackets and moving parts
- Recheck any earlier harness repair, because untwisted or poorly joined CAN pairs are a common cause
- After the repair, clear the codes and confirm the module leaves single-wire mode and communication stays stable on a road test