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 control unit engages the fan clutch when the engine gets hot.
- First, on your own: inspect the fan clutch connector and wires and check the fuse.
- FMI 3, 4, 5 — an open or short in the clutch circuit.
- Watch the temperature gauge: if the fan doesn’t come on and the engine is heating up, stop and switch off the engine.
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
OOleg’s tip: check the connector
Often the cause is simple — there is no contact in the connector (plug). Look at the connector from the back: remove the rubber seal and you will see whether a wire is corroded or has come off completely. Corrosion shows up as green deposits. Ideally, gently pull each wire towards you one at a time: a sound wire stays in place, while a corroded one simply comes off — it needs to be repaired.
Unplug and inspect connectors with the ignition off.
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.