A fault code doesn’t yet mean the unit or sensor itself is faulty: often it’s the plug and connector leading to it.
What you can do yourself
- Check the AdBlue level, the AdBlue pump filter and lines — they can freeze in winter.
- FMI 3, 4 — the AdBlue pressure sensor (usually in the pump module), its connector or wiring.
- FMI 7 — the pump doesn’t build working pressure: level, pump filter, lines, air leaks.
Stop and don’t drive on if:
- The Check Engine light is flashing
- The temperature gauge is in the red or the overheating light is on
- The red oil pressure light is on
- Smoke from under the bonnet, a burning or petrol smell
- Strong jerking, knocking from the engine, or the car barely moves
Add the FMI — the second number of the code. It shows what exactly is wrong with the parameter.
Source: Detroit DDC-SVC-MAN-0084: SPN 4334 (static.nhtsa.gov, MC-10142005)
The explanation comes from the error code reference in the AvtoElektrik PRO app.