U029DLost Communication With 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 is normally the engine-out or SCR inlet sensor; its control unit puts NOx and oxygen values on CAN. U029D means these frames have stopped. GM treats it as Type A: its 2016 diesel tables wait 10 s, the 2025 tables (25OBDG04A/B) about 1 s for most frames, at 11 to 18 V with the bus otherwise healthy; on the 2014 6.6 L LML the code also counted checksum errors. Ford's 2023 diesel summary allows just over 1 s. Ford found water in the sensor module plug of 6.7 L F-Super Duty trucks from 2017-2019 and replaced module and harness 14406 (TSB 18-2365). Volvo and Mack name fuses, supply, J1939 wiring and terminating resistors, and on 2023 trucks a start-up timing bug. Deutz uses U029D for the upstream SCR sensor. MIL, open SCR checks and derate are possible.
- What you may notice
- MIL on
- SCR or NOx monitor not completed
- Engine derate on some trucks
- Likely causes
- LikelyWater or corrosion in the NOx sensor module connector or harness
- PossibleBlown fuse, open supply or ground of the sensor module
- PossibleSensor CAN wiring damaged or terminating resistor faulty
- PossibleEngine control software with start-up timing fault
- RareNOx sensor 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: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.