What does it mean?
U1135 is a Network (CAN bus, module communications) fault code. It indicates: Data Circuit Message .
Symptoms
- Intermittent no-crank or no-start, often cured by moving the key slightly
- Engine or accessories cutting out while driving, sometimes with the dash going dark for a moment
- Warning lamps flickering and modules resetting during cranking
- Radio, wipers or climate control losing power in certain key positions
- Battery drain because modules never see the ignition go off and stay awake
- Communication codes stored in several modules at the same time
Likely causes
- Worn electrical section of the ignition switch, with intermittent contact in the run or start position
- Blown fuse or a corroded terminal in the ignition feed circuit
- Broken or shorted wiring between the ignition switch and the modules that receive its status
- Poor connection at the starter relay or ignition relay in the fuse box
- Aftermarket remote start or alarm wiring tapped into the ignition circuits
- Body control module fault, so it does not broadcast the ignition status
- Voltage drop caused by a weak battery or corroded main connections during cranking
How to fix it
- Read the ignition status parameter in live data while turning the key through each position
- Check the ignition feed fuses and measure voltage at the switch output in accessory, run and start
- Perform a voltage drop test across the ignition switch and its connector while the circuit is loaded
- Inspect any aftermarket remote start or alarm wiring and disconnect it to see whether the fault clears
- Check the ignition and starter relays and their sockets for burnt or spread terminals
- Test battery condition and main cable connections, because voltage collapse during cranking can set this code
- Replace the ignition switch electrical section if it fails testing, and address body control module faults only after the switch and wiring test good