Faulty NOx sensor itself, sending erratic or out-of-range data.; Damaged or corroded wiring or connector at the NOx sensor or ECM/PCM.; Software or calibration issue in the ECM/PCM causing it to misinterpret valid sensor data.; Exhaust leaks before the NOx sensor allowing air to skew readings.; Contaminated sensor element from excessive soot or oil ash.; Low DEF quality or level affecting NOx reduction and sensor feedback.; Internal ECM/PCM fault, though rare.

DTC codes / U05xx · Network communication / U05A2

U05A2NOx Sensor B Received Invalid Data From ECM/PCM

Q: What does code U05A2 mean?

NOx Sensor B Received Invalid Data From ECM/PCM. This code means the engine control module (ECM) or powertrain control module (PCM) has received data from a nitrogen oxide (NOx) sensor that it considers invalid or out of range. The NOx sensor is reporting a signal the computer cannot trust, so it flags the communication as faulty rather than a simple sensor failure.

This code means the engine control module (ECM) or powertrain control module (PCM) has received data from a nitrogen oxide (NOx) sensor that it considers invalid or out of range. The NOx sensor is reporting a signal the computer cannot trust, so it flags the communication as faulty rather than a simple sensor failure.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
Reduced engine power or limp mode in some vehicles as a protective measure.
Poor fuel economy or increased diesel exhaust fluid (DEF) consumption.
Rough running or hesitation if the invalid data affects fuel delivery or emissions control.
Failed emissions test due to the stored fault code.

Common causes, most likely first

Faulty NOx sensor itself, sending erratic or out-of-range data.
Damaged or corroded wiring or connector at the NOx sensor or ECM/PCM.
Software or calibration issue in the ECM/PCM causing it to misinterpret valid sensor data.
Exhaust leaks before the NOx sensor allowing air to skew readings.
Contaminated sensor element from excessive soot or oil ash.
Low DEF quality or level affecting NOx reduction and sensor feedback.
Internal ECM/PCM fault, though rare.

How to diagnose and fix it

Use a scan tool to retrieve all stored codes and freeze-frame data, then clear codes and test-drive to see if U05A2 returns.
Visually inspect the NOx sensor wiring and connector for chafing, corrosion, or loose pins, and repair as needed.
Check for exhaust leaks upstream of the NOx sensor and repair any found.
Verify DEF quality and level, and perform a DEF system test if applicable.
Monitor live NOx sensor data on a scan tool to see if readings are plausible and within range.
If data is invalid, substitute a known-good NOx sensor and recheck; replace sensor only if confirmed faulty.
If the sensor and wiring are good, check for ECM/PCM software updates or reprogramming per manufacturer procedures.

What the invalid data really means

The ECM/PCM flags U05A2 when the NOx sensor's signal is outside the expected range or inconsistent with other sensor inputs, not necessarily when the sensor is dead.
A weak battery or charging system issue can cause momentary voltage drops that corrupt sensor data and set this code intermittently.
Aftermarket NOx sensors or incorrect replacements often produce invalid data that triggers this code even though the sensor is new.
Exhaust system modifications or leaks can introduce air that makes the NOx sensor report values the ECM/PCM rejects as invalid.
The code can be stored alongside other NOx or DEF codes, so always diagnose the root cause rather than replacing parts based on U05A2 alone.

Can I keep driving with U05A2?

You can usually continue driving with this code, but avoid heavy loads or long trips until it is diagnosed because invalid NOx data can lead to increased emissions and possible limp mode. If the engine enters reduced power mode, seek service promptly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.