U05A8Invalid Data Received From NOx Sensor C
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- A third NOx sensor appears on exhaust systems with two SCR stages, where sensor C watches the gas after the second catalyst. GM's 2025 ECM tables (25OBDG04B) are the public example: the engine controller checks alive rolling count and checksum of the post-second-catalyst NOx signals, eight failures in 18 samples or three in ten depending on the signal, with battery voltage of at least 11 V for 5 s, and logs U05A8 as Type B. The companion 25OBDG04A set has no such entry. U02A1 covers loss of sensor C messages, U05A9 the case where sensor C refuses engine data, U059E and U059F the first two sensors. The second SCR stage cannot be judged while the code is present.
- What you may notice
- Check engine light after two trips
- SCR monitor for the second catalyst incomplete
- Likely causes
- LikelyControl unit of NOx sensor C faulty
- PossibleHarness or connector of the rearmost sensor damaged
- RareSensors swapped between positions during repair
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €150 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.