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
- The AdBlue lines are heated electrically so the AdBlue doesn’t freeze. If the heating fails, in winter the pump can’t build pressure and the engine may limit power.
- First, on your own: inspect the heated line connectors at the pump and at the dosing valve, and check the AdBlue heater fuse and relay.
- FMI 5 — an open in the line heater circuit: the connector or the heater element in the line itself.
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 4355 (static.nhtsa.gov, MC-10129728)
The explanation comes from the error code reference in the AvtoElektrik PRO app.