U011B — Lost Communication With Rocker Arm Control Module "A"

vehicle network

Is it safe to drive?

Drive with caution Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

How to diagnose with an OBD scanner

  1. Read the code and freeze frame Connect an OBD2 scanner, confirm U011B is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the vehicle network (CAN bus) communication for damage, corrosion, chafing or poor contact.
  4. Subsystem check Measure resistance between CAN-High and CAN-Low at the OBD port with power off — about 60 Ω is healthy.
  5. Subsystem check Scan all modules: the one that does not respond is either the culprit or downstream of the break.
  6. Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U011B does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for U011B (parts and labor, USD, independent shop rates): Repair CAN wiring or connectors: $100–$400; Replace the faulty control module: $300–$1,500; Remove interfering aftermarket device: $0–$150. Overall, fixing U011B usually costs between $0 and $1,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Will U011B clear itself?

Sometimes U011B clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

Is it safe to drive with U011B?

Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

What does OBD2 code U011B mean?

Lost Communication With Rocker Arm Control Module "A" (U011B): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by corroded connectors, especially in wet areas, water ingress in harness junctions, poor grounds or low battery voltage.

How much does it cost to fix U011B?

Repair CAN wiring or connectors — $100–$400; Replace the faulty control module — $300–$1,500; Remove interfering aftermarket device — $0–$150. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What is the most common cause of U011B?

The most common causes are: corroded connectors, especially in wet areas, water ingress in harness junctions, poor grounds or low battery voltage.

What does U011B mean?

Seeing U011B on your scanner? The control unit has caught the vehicle network (CAN bus) communication operating outside its calibrated window. The formal description is “Lost Communication With Rocker Arm Control Module "A"”, and the code is grouped under vehicle network faults.

The module monitors this system continuously while driving. When readings fall outside the expected range for a defined number of drive cycles, it stores U011B and switches on the warning light. Freeze frame data saved with the code shows the exact conditions — rpm, load, temperature, speed — at the moment the fault was detected, which is the best starting point for diagnosis.

What causes U011B?

  • water ingress in harness junctions
  • corroded connectors, especially in wet areas
  • poor grounds or low battery voltage
  • aftermarket equipment interfering with the bus

Common symptoms of U011B

  • modules intermittently not communicating with the scanner
  • random, hard-to-reproduce electrical glitches
  • intermittent loss of functions (gauges, windows, steering assist)
  • no-start or intermittent starting in some cases
  • multiple warning lights on at once

How to diagnose U011B

  1. Connect an OBD2 scanner, confirm U011B is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Visually inspect the wiring harness and connectors related to the vehicle network (CAN bus) communication for damage, corrosion, chafing or poor contact.
  4. Measure resistance between CAN-High and CAN-Low at the OBD port with power off — about 60 Ω is healthy.
  5. Scan all modules: the one that does not respond is either the culprit or downstream of the break.
  6. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U011B does not return.

How to fix U011B

Start with the cheapest and most common causes before replacing expensive parts:

  • Repair CAN wiring or connectors — $100–$400
  • Replace the faulty control module — $300–$1,500
  • Remove interfering aftermarket device — $0–$150

How much does it cost to fix U011B?

Repair cost depends on which component actually failed. Typical scenarios for U011B (parts and labor, USD, independent shop rates):

  • Repair CAN wiring or connectors: $100–$400
  • Replace the faulty control module: $300–$1,500
  • Remove interfering aftermarket device: $0–$150

Overall, fixing U011B usually costs between $0 and $1,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with U011B?

Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

Related OBD2 codes