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 tank is heated by engine coolant: a valve opens the coolant flow when the AdBlue is cold. Without heating, AdBlue freezes at −11 °C.
- First, on your own: check the coolant level, the hoses to the AdBlue tank and the heater valve connector.
- FMI 3, 4, 5 — an open or short in the valve circuit: connector and wires.
- FMI 1 — the tank doesn’t warm up; FMI 16 — it gets hotter than it should: the valve doesn’t close, or the coolant hoses to the tank were swapped during a repair.
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: Navistar IK0700079: DEF Tank Heater, DEF Quality (static.nhtsa.gov, MC-10162033)
The explanation comes from the error code reference in the AvtoElektrik PRO app.