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
- FMI 1, 17, 18 — low AdBlue: top it up.
- FMI 3, 4, 5 — level sensor or wiring.
- FMI 19 — the level value isn’t arriving over the CAN bus: check the level sensor connector on the AdBlue tank and its wires.
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 IK0800520: SPN 1761, 3216, 3226 FMI 19 (static.nhtsa.gov, MC-10117065)
The explanation comes from the error code reference in the AvtoElektrik PRO app.