U029E code meaning
Lost Communication With NOx Sensor B
Network system Generic code U02xx codes Check engine light
What U029E means
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.
U029E at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.3 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of U029E
- MIL on
- SCR efficiency monitor not completed
- Engine derate on some heavy trucks
Common causes of U029E
- Most 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
- Less likelyNOx sensor B control unit internally failed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nox sensor bVehicle bus wiring
What each part of U029E means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 9E | The exact fault in that area. |
What to do next
- Note U029E and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U029E
What does U029E mean?
U029E means "Lost Communication With NOx Sensor B". Sensor B usually measures NOx at the outlet, behind the SCR catalyst, so the SCR efficiency verdict depends on it. It is a generic code, so it means the same on every make.
Is it safe to drive with U029E?
Drive gently and only to a workshop. With U029E the car can go into limp mode (reduced power) to protect itself.
Will U029E fail an emissions test?
Yes, it can. U029E is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U029E to fix?
Difficulty: medium. A typical repair takes 0.3 to 3 hours of work. This is a job for a workshop.
Will U029E clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.