U011B: Lost Communication With Rocker Arm Control Module A
What does U011B mean?
U011B is a network communication fault logged when the main control system loses contact with Rocker Arm Control Module A over the CAN communication bus. The rocker arm control module manages variable valve actuation systems, which adjust valve timing and lift to optimise engine performance and efficiency across different operating conditions. When this module drops off the bus, the ECU has no data from it and logs U011B.
Common causes include a wiring fault or open circuit in the CAN bus wiring to the module, a failed module, a blown fuse protecting the module's power supply, or a connector that has worked loose or corroded. Start by checking the module's fuse, inspecting the connector for damage, and looking at the wiring harness for any obvious chafing or breaks.
The fault is rated low severity, meaning the vehicle will typically remain driveable, but the engine may lose the benefits of variable valve actuation which can reduce performance and fuel economy. If additional codes are present alongside U011B, address those first as they may point to a shared root cause. Clear the fault after inspection and confirm whether it resets before committing to further repairs.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Possible issues with communication bus operation
- Vehicle may enter reduced power mode (limp mode)
Estimated repair cost
Typical range in Australia (parts + labour)
Common causes
- Failed control module
- CAN bus wiring fault or short
- Blown fuse to the affected module
- Water intrusion in a connector or module
- Battery voltage too low
What should you do?
This is a minor or informational code. Monitor for any changes in vehicle behaviour and address it during your next scheduled service visit.
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