What does it mean?
U1109 is a Network (CAN bus, module communications) fault code. It indicates: Lost Communication with Rear Active Stabilizer ECU .
Symptoms
- Suspension or stability warning lamp with a message that the roll control system is unavailable
- Noticeably more body roll in corners and a floaty feel during quick lane changes
- Ride quality changes, sometimes harsher or uneven from side to side
- The fault appears mainly in cold or wet weather and may clear once things dry out
- The stabilizer module does not answer the scan tool
Likely causes
- Corroded or water damaged connector at the rear stabilizer actuator or its control unit, which sits in an exposed underbody location
- Blown fuse or a failed power feed or ground at the stabilizer control unit
- Chafed or broken harness along the rear subframe, where road debris, salt and suspension movement attack the wiring
- Internal fault in the actuator that makes its control unit shut down and stop transmitting
- Damaged bus wiring at the rear of the vehicle, sometimes after underbody or exhaust work
- Low system voltage or a weak battery causing the module to drop off the bus
- Failed stabilizer control unit
How to fix it
- Check whether the code is current or stored in history, then try to reproduce it with the scan tool connected
- Inspect the rear stabilizer control unit and actuator connectors for water, corrosion and green terminals
- Verify the fuse, battery feed and ground at the module connector with the circuit loaded, not just with a test lamp
- Follow the harness along the subframe and suspension for chafing, stretched sections and rodent damage
- Measure the bus lines at the module connector and compare them with a module that is communicating normally
- Test battery and charging output, since this module drops offline early when voltage sags
- Repair the wiring or connector, and replace the control unit only once power, ground and bus lines are proven good