U05A1
NOx Sensor A Received Invalid Data From ECM/PCM
NOx sensor A (smart sensor with own ECU) received implausible data from the ECM/PCM. Engine load, fuel rate or temperature data needed for the sensor's internal compensation fails plausibility checks; the sensor reports degraded readings.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
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
Common causes
Ordered by how often each turns out to be the cause.
- ECM/PCM internal fault or sensor input driftCommon
- Software version mismatch after replacementPossible
- Gateway module routing CAN messages incorrectlyLess likely
Parts involved
- NOX Sensor A
- ECM
U05A1 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.