OBD-II code · Network
U029D Lost Communication With NOx Sensor A
The vehicle bus reports loss of communication with NOx sensor A (smart sensor with own ECU). The SCR catalyst control loop loses its actual NOx feedback and may switch to substitute values.
Is it safe to drive with U029D?
The car may go into limp mode (reduced power). Get it diagnosed before a long trip.
Common causes
- Most likelyBus wiring open or shorted
- PossibleModule without power or ground
- PossibleModule failed
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–3 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Nox Sensor A, Vehicle Bus Wiring
Related codes
- U029ELost Communication With NOx Sensor B
- U02A1Lost Communication With NOx Sensor C
- U029ALost Communication With Hybrid/EV Battery Pack Sensor Module
- U029BLost Communication With Drive Motor Control Module C
- U029CLost Communication With Drive Motor Control Module D
- U029FLost Communication With Evaporative Emission System Leak Detection Control Module
- U02A0Invalid Data Received From Hybrid/EV Battery Interface Control Module D
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.