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 main relay powers the engine control unit and sensors once the ignition is switched on.
- First, on your own: check the relay and its fuse. You can swap it with an identical working relay and see whether the code goes away.
- FMI 3, 4, 5 — an open or short in the relay coil circuit.
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: SAE J1939-71: J-1939 SA/SPN/FMI Descriptions (static.nhtsa.gov, MC-10141869)
The explanation comes from the error code reference in the AvtoElektrik PRO app.