U02A1Lost Communication With 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, C, is fitted where the aftertreatment needs one more measuring point, typically behind a second SCR stage. U02A1 is set when its CAN messages no longer reach the engine controller. GM's 2025 tables (25OBDG04B) wait longer than 10 s without any of its five messages, with 11 to 18 V and the bus up, and rate it Type B, so the MIL comes on after the second failed trip; the sibling codes for sensors A and B are Type A there. GM also lists U02A1 in bulletin 21-NA-149 among codes caused by chafed engine harnesses on 3.0 L LM2 diesel trucks and SUVs. Ford's SSM 51750 links it on 2023 F-Super Duty 6.7 L to a harness 14406 rubbing on the EGR cooler near C146; first check 20 A fuse F18. The second SCR stage then goes unchecked.
- What you may notice
- MIL on after two drives
- Further NOx or PM sensor codes stored at the same time
- SCR monitor for the second stage incomplete
- Likely causes
- LikelyEngine harness chafed on a hot component such as the EGR cooler
- PossibleBlown fuse feeding the NOx sensor modules
- PossibleWater or corrosion at the sensor C connector
- RareNOx sensor C control unit internally failed
- 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: €20 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.