U059EInvalid Data Received From NOx Sensor A
- 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
- NOx sensor A usually sits upstream of the SCR catalyst. Its attached electronics turn the probe current into NOx and oxygen readings and broadcast them on CAN. Here those frames still arrive, yet the receiver rejects them. GM's 2025 diesel ECM tables (25OBDG04A/B) count wrong alive rolling counts, protection values or checksums: 8 bad out of 18 samples for most signals, 3 out of 10 for a few, with at least 11 V present for 5 s. It is Type B, so the MIL follows on the second trip. Ford's 2023 diesel summary sets it when the sensor's calibration verification number never reaches the ECU. U029D stands for a silent sensor, U05A1 for the reverse path. Until valid readings return, NOx-based SCR checks and dosing feedback cannot run.
- What you may notice
- Check engine light after the second faulty trip
- SCR and NOx sensor monitors stay incomplete
- Engine usually runs normally
- Likely causes
- LikelySensor control unit of NOx sensor A faulty (heat, moisture, internal error)
- PossibleReplacement sensor of a different part number or software level
- PossibleCorroded connector or damaged CAN/supply wiring at the sensor
- RareEngine controller software needing an update
- 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.