OBD-II · Engine and powertrain (P)
P204F
AdBlue (reductant) system performance bank 1
What it means
The AdBlue system as a whole is not performing as expected - dosing, pressure or NOx reduction does not match what the computer asks for. 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
- AdBlue/emissions warning, possibly with a no-start countdown
- engine warning light
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | dosing injector blocked by crystals |
| 02 | weak AdBlue pump or blocked filter |
| 03 | leaking or crystallised line |
| 04 | poor-quality AdBlue |
| 05 | NOx sensor fault |
What to check, step by step
- 01Read all other SCR codes first - they usually narrow it down.
- 02Check AdBlue level and quality.
- 03Inspect the dosing injector and lines for crystals and leaks.
- 04Run pump pressure and dosing quantity tests with a diagnostic tool.
- 05Check NOx sensor live data.