U011B code meaning
Lost Communication With Rocker Arm Control Module A
Network system Generic code U01xx codes Check engine light
What U011B means
U011B covers the first rocker arm control module. On overhead-cam engines that shut cylinders down or change valve lift, a solenoid routes engine oil to unhook a pin coupling two rocker arms; the cam-driven arm then moves on its own and the valve stays shut. Where a maker hands this switching to a dedicated controller, the engine controller sets U011B when that unit's messages stop. No manufacturer documents the code publicly. CARB requires lost digital communication to be coded separately and also obliges makers to supervise systems that vary valve timing or lift. U011C is the second module, U041C stands for invalid data from this one. Expect the MIL, switching of valve lift or cylinder deactivation locked out and higher fuel use.
U011B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor1 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of U011B
- MIL on
- Cylinder deactivation or valve lift switching inactive
- Higher fuel consumption
Common causes of U011B
- Most likelyRocker arm module without power or ground
- PossibleOil-soaked or heat-damaged connector on the cylinder head
- PossibleDamaged CAN wiring between module and engine controller
- Less likelyRocker arm control module internally faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Rocker arm module aCAN bus wiring
What each part of U011B means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 1B | The exact fault in that area. |
What to do next
- Note U011B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U011B
What does U011B mean?
U011B means "Lost Communication With Rocker Arm Control Module A". U011B covers the first rocker arm control module. It is a generic code, so it means the same on every make.
Is it safe to drive with U011B?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U011B fail an emissions test?
Yes, it can. U011B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U011B to fix?
Difficulty: medium. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will U011B clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.