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OBD-II · Engine and powertrain (P)

P2BAD

NOx exceedance - root cause unknown

What it means

NOx emissions exceed limits and the system cannot identify a specific cause. On vehicles with SCR, a confirmed unresolved fault may trigger reduced performance or a no-restart countdown; follow the displayed warning and the vehicle handbook.

Symptoms

  • emissions warning; an AdBlue no-start countdown may appear on SCR-equipped vehicles
  • engine warning light
  • if a no-start countdown is displayed, restarting is inhibited when it reaches zero

Likely causes, most likely first

Likely causes, most likely first
No.Cause
01poor AdBlue quality
02dosing injector partly blocked
03NOx sensor drift
04aged SCR catalyst
05EGR fault

What to check, step by step

  1. 01Check AdBlue quality and level.
  2. 02Inspect the dosing injector and run a dosing test.
  3. 03Compare NOx sensor readings before and after the catalyst.
  4. 04Check EGR operation.
  5. 05Work through any other stored codes first.