What does it mean?
U1105 is a Network (CAN bus, module communications) fault code. It indicates: CAN B Signal Missing .
Symptoms
- Warning lamps on the dash, often several at once rather than a single one
- Multiple U-codes stored across different control modules
- Gauges, indicators or driver information messages dropping out intermittently
- Body electronics such as lighting, central locking or climate control responding slowly or not at all
- Scan tool cannot establish communication with one or more modules
- Parasitic battery drain if modules stay awake because the bus never goes to sleep
Likely causes
- Open circuit, short to ground or short to battery in the CAN B wiring between the chassis module and the rest of the network
- Corroded, spread or backed-out terminals in a bus connector, or a loose body ground point
- The module that broadcasts chassis status data is unpowered because of a blown fuse or a failed power or ground feed
- One faulty module loading the bus and blocking other messages from getting through
- Water intrusion into a bulkhead, under-carpet or door-sill connector
- Gateway module fault, so the message never crosses from the body bus to the requesting bus
- Configuration or software mismatch after a module was replaced or reprogrammed
How to fix it
- Record freeze frame data, then scan every module in the vehicle and note which ones answer and which do not
- Test battery state of charge and charging system output first, since low or noisy voltage alone can set bus codes
- Visually inspect the body harness, bulkhead connectors and ground straps for corrosion, chafing, rodent damage or water
- Back-probe the CAN B lines and check voltage levels and bus resistance, performing a wiggle test on suspect sections
- Disconnect modules one at a time to see whether communication is restored, which identifies the module dragging the bus down
- Repair the wiring or connector found, clear the codes and confirm the fault does not return over several drive cycles
- Only after wiring and power feeds are proven good, check for a control module software update or replace the failed module and configure it