U029ELost Communication With NOx Sensor B
- 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
- Sensor B usually measures NOx at the outlet, behind the SCR catalyst, so the SCR efficiency verdict depends on it. U029E is logged once its CAN messages fail to reach the engine controller. GM monitors the post-catalyst frames the same way as for sensor A and also treats a loss as Type A; Ford's 2023 diesel summary reacts after more than 1 s, and Ford's 2014 code list shows it with MIL. Typical causes are installation errors: Volkswagen's tech tip 01-18-09TT for the 2015 Golf, Jetta, Passat and Beetle 2.0 TDI tells technicians who see U029E after campaign 23Y8 to look for swapped plugs at the front sensor and its adapter and an unseated rear sensor plug. Ford's SSM 50455 ties it on 2021 F-Super Duty 6.7 L to an incomplete PCM reprogramming. The tailpipe check stays open.
- What you may notice
- MIL on
- SCR efficiency monitor not completed
- Engine derate on some heavy trucks
- Likely causes
- LikelySensor plugs swapped or not fully seated after service work
- PossibleWater or corrosion in the NOx sensor connectors
- PossibleIncomplete or wrong engine control module programming
- RareNOx sensor B 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: €0 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.