U041D: Invalid Data Received From Rocker Arm Control Module B

What it means

A control module received data from Rocker Arm Control Module B that it judged invalid or implausible. This code identifies the rejected data, but does not by itself identify the cause.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

Rocker Arm Control Module B manages a rocker-arm system that can alter valve operation on some engines. Other modules check the data it sends over the vehicle network for plausibility; U041D sets when a receiving module rejects data from module B.

Common causes

Most likely first.

1. Fault or implausible input at Rocker Arm Control Module B
2. Damaged or loose network wiring or connector
3. Module power, ground, or programming issue

Symptoms

• Check-engine light may illuminate
• Engine operation may be affected
• Other communication codes

How to diagnose it

1. Scan all modules and record freeze-frame data and related codes to see whether the fault is isolated to module B or part of a wider network or power problem.
2. Check whether the engine has symptoms such as reduced power or rough running, and note any rocker-arm or valve-control codes that could explain implausible module B data.
3. Inspect module B's connectors and network wiring for looseness, corrosion, fluid intrusion, chafing, or damage.
4. Check module B's power and ground circuits under the conditions specified by the manufacturer, since low or unstable supply can disrupt its messages.
5. Use a scan tool to compare module B data with related engine data and check network communication; test the bus and module circuits to the manufacturer's specification.
6. If wiring, power, and network checks pass, verify applicable software or calibration updates before considering module replacement.

Common fixes

• Reconnect or repair a loose, corroded, or damaged module B connector.
• Repair damaged network wiring to the rocker arm control module.
• Repair module B power or ground faults.
• Correct an applicable software or calibration issue.
• Replace module B if its inputs and circuits test correctly but its data remains invalid.

Can I keep driving?

If the engine runs normally and no warning indicates reduced power, drive gently and arrange diagnosis soon. Avoid hard acceleration if power or engine operation is affected; a rocker-arm control fault can worsen drivability and may lead to engine damage.