Lost Communication with NOx Sensor B
What does DURAMAX-U029E mean?
The DURAMAX-U029E (Duramax) diesel fault code means: Lost Communication with NOx Sensor B. This is a serious severity code.
Common Symptoms
- Check Engine Light illuminated
- Performance loss or rough running (if engine-related)
- Warning message on dash (DPF/DEF-related)
- Limp mode under certain conditions
- Possible hard starting or stalling
Probable Causes (Ranked by Likelihood)
- Downstream NOx sensor comms lost Very Likely
- Wiring harness abrasion / connector corrosion Likely
- Sensor end-of-life (high-mileage trucks) Possible
- Related upstream fault (e.g., low battery voltage, ground fault) Possible
Step-by-Step Diagnostic Procedure
Scan all modules — a single failure often sets codes in multiple modules
Capture freeze frame and compare to known operating ranges
Back-probe the associated sensor/actuator with a DMM
Inspect wiring and connectors at both ends of the affected circuit
Clear code, perform a complete drive cycle, and verify the fault is fixed
Frequently Asked Questions
What is U029E on a Duramax?
Duramax code U029E (Lost Communication with NOx Sensor B) is a serious-severity diagnostic trouble code triggered by the engine control module when it detects a problem in the associated system. Duramax trucks accumulate soft-fault codes — clear them and retest rather than throwing parts at recurring-but-harmless DTCs.
Is a Duramax U029E safe to drive?
Depends on severity. Critical codes (fuel pressure, PCM, overtemp) need immediate attention. Sensor codes are usually OK short-term.
How much does it cost to fix U029E on a Duramax?
Typical repair cost $300-$600. Scan first — cascaded codes often share a single root cause.