What does it mean?
U1106 is a Network (CAN bus, module communications) fault code. It indicates: CAN C Signal Missing .
Symptoms
- Check engine lamp on and readiness monitors that never complete
- Scan tool cannot read live data, or connects to some modules only
- Emissions inspection fails because the required diagnostic data is unavailable
- Rough running, limp mode or reduced power when powertrain modules lose shared data
- Transmission shifting harshly or defaulting to a fixed gear
- Additional communication codes stored in the ABS, cluster or transmission modules
Likely causes
- Open or shorted CAN C high or low wire between the powertrain modules and the diagnostic connector
- Missing or out-of-tolerance termination, so the bus cannot hold a stable signal
- Powertrain control module without a proper battery feed, ignition feed or ground
- A module on the high-speed bus that has failed internally and is pulling one of the lines up or down
- Damaged pins in the diagnostic socket or in an engine bay connector exposed to heat and moisture
- Aftermarket electronics wired into the bus, such as tracking, alarm or tuning devices
- Corroded splice or repair joint in the CAN twisted pair
How to fix it
- Confirm which modules respond to the scan tool and which are silent; the missing ones point to the damaged bus section
- With the ignition on and the engine off, measure both CAN C lines against ground and confirm they sit near their normal resting level
- Measure resistance across the CAN pair with the battery disconnected; roughly 60 ohms indicates both terminating resistors are present
- Inspect the diagnostic connector, engine bay connectors and any repair splices for corrosion, spread terminals and heat damage
- Remove aftermarket devices connected to the bus and retest
- Disconnect modules one by one until the bus recovers, which isolates the failed unit
- Repair the harness, then clear codes and verify normal communication and completed monitors on a road test