What it means
A receiving module detected implausible data tagged as emissions-critical (CARB OBD requirement). The receiver discards the message and may set the MIL because emissions monitors cannot run.
At a glance
- Usually lights the warning light of the system that lost communication
- Affects emissions; the car can fail an emissions test
How it works
Emissions-critical control information is shared between modules so the vehicle can manage emissions functions and OBD monitoring. U0441 is set when a receiving module rejects data identified as emissions-critical because it fails plausibility checks; emissions monitoring may be affected even if the engine seems to run normally.
Common causes
Most likely first.
- Module internal fault or sensor input drift
- Software version mismatch after replacement
- Gateway module routing CAN messages incorrectly
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and save freeze-frame data, emissions-related codes, and communication faults to identify the rejected information's source and receiver.
- Check readiness and emissions live data to see which monitors or reported values are unavailable or implausible.
- Inspect connectors and wiring at the source and receiving modules for corrosion, looseness, damage, or evidence of recent repairs.
- Check for gateway and network faults that could disrupt delivery of emissions-critical messages.
- If a module was replaced or updated, verify compatible software and configuration, then test the affected modules using the manufacturer's diagnostic procedure.
Common fixes
- Repair a loose, corroded, or damaged connector or network wire identified during inspection.
- Correct a gateway communication fault confirmed by testing.
- Update or configure a replacement module to the vehicle's required software.
- Repair a confirmed fault in the module supplying the emissions-critical data.
- Replace a receiving module only after diagnosis confirms it is rejecting valid data.
Can I keep driving?
The vehicle may drive normally, but emissions monitors may not complete and the warning may affect inspection readiness. Avoid clearing codes before diagnosis, since that resets monitor progress, and address any rough running or additional engine warnings promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.