U05A2: NOx Sensor B Received Invalid Data From ECM/PCM

What it means

NOx sensor B (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.

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

NOx sensor B has its own electronics and relies on engine data from the ECM/PCM, such as load, fuel rate, and temperature, to compensate its readings. U05A2 is set when sensor B judges the engine data it receives from the ECM/PCM implausible and reports degraded NOx readings.

Common causes

Most likely first.

1. ECM/PCM internal fault or sensor input drift
2. Software version mismatch after replacement
3. 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

1. Scan all modules and save freeze-frame data to identify related ECM/PCM, sensor B, exhaust-temperature, SCR, and communication faults.
2. Review live data received by NOx sensor B and compare engine load, fuel-rate, and temperature values with the ECM/PCM's corresponding data for gaps or contradictions.
3. Locate sensor B according to the exhaust layout and inspect its connector and harness, plus the ECM/PCM connections, for damage, corrosion, moisture, or recent disturbance.
4. Check the communication path and module power and grounds using the manufacturer's procedure, focusing on data sent from the ECM/PCM to sensor B.
5. If the ECM/PCM, sensor B, or gateway was recently replaced or updated, verify software compatibility and configuration.
6. If the ECM/PCM's reported engine values are themselves implausible, diagnose their source before replacing sensor B; otherwise follow the manufacturer's procedure to isolate the communication or receiving-sensor fault.

Common fixes

• Repair damaged wiring or secure the ECM/PCM and sensor B connectors.
• Resolve the underlying engine sensor or ECM/PCM data fault if the transmitted values are incorrect.
• Correct module software or configuration after a replacement or update.
• Replace NOx sensor B only if the ECM/PCM data and communication path are valid but sensor B still rejects them.

Can I keep driving?

Drive only as needed if the vehicle runs normally, and arrange prompt diagnosis because sensor B may report degraded emissions data. Avoid heavy loads if power is limited, and stop if a warning indicates the vehicle should not continue.