U011B–U011C Lost Communication With Rocker Arm Control Module A
This module has stopped talking on the car's data network, so nothing else can hear it.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
U011B | Lost Communication With Rocker Arm Control Module A | Investigate soon |
U011C | Lost Communication With Rocker Arm Control Module B | Investigate soon |
The definition
U011B: Lost Communication With Rocker Arm Control Module A.
U011B is a network code (communication between control modules), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Check power and earth at the module first - a module with no supply cannot answer.
- Check the two data-bus wires for continuity and for a short between them.
- Scan the other modules: if several report the same module missing, the fault is at that module rather than on the bus.
What actually causes this on a VAG
This is a generic code from the industry-wide list, describing a separate control unit for a rocker arm or valve lift system that has stopped communicating. VAG's own variable valve lift and cylinder deactivation systems are controlled directly by the engine ECU rather than by a standalone module on a data network, so this description does not map cleanly onto these cars. In plain terms: be sceptical of the code's name and find out what the car's own diagnostics actually say before anyone starts opening the engine.
Most likely causes, in order
- A generic scan tool mis-translating a VAG fault. Cheap readers convert manufacturer-specific faults into the closest generic wording, which can produce a description that has nothing to do with the real problem. Get the car scanned with a tool that reports VAG's own fault text, the affected module and freeze-frame data, and work from that.
- Wiring, connector or supply fault at a valvetrain actuator. If a genuine valvetrain-related fault is confirmed by a proper scan, the cheap end is always checked first: the plug fully home, insulation not chafed or heat-damaged, pins not corroded, fuse and earth intact.
- Weak battery or an unstable supply. Low voltage causes modules to drop off and log communication faults that look far more dramatic than they are. If several unrelated communication codes are stored together, test the battery and charging system before anything else.
Worth knowing: Do not authorise valvetrain or cylinder head work on the strength of this code alone. Insist on a VAG-specific scan showing the real fault in the manufacturer's own wording, plus supporting live data, before any part of the engine is opened up.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
$249 once. No subscription, unlimited cars. Windows 10/11.
See VAGPULSE — $249 Look up another codeSoftware downloads instantly · cable ships September 30 · cable guarantee — refund if it won't connect
Prefer to work on your phone? The VAGPULSE Android app is a free download and its demo mode runs against a sample car with no hardware at all, so you can see exactly what it reads before spending anything. Reading your car with it needs the VAGPULSE cable, which comes with the licence.
Common questions
What does U011B mean?
U011B means Lost Communication With Rocker Arm Control Module A. This module has stopped talking on the car's data network, so nothing else can hear it.
Can I drive with U011B?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.