What does it mean?
Here the charge air cooler cooling fan circuit is electrically in order, but the fan is not producing the effect the module expects. The software commands the fan and then looks for confirmation: falling intake air temperature, a speed or current feedback signal, or both. When the command is present and the circuit is intact yet nothing changes, the fan is judged to be stuck off or performing poorly. This is a mechanical or load related failure rather than a wiring fault, so the diagnosis begins with confirming whether the fan physically turns and moves air. Without it, intake temperatures rise at low vehicle speed exactly when boost demand is often highest, so the module protects the engine by cutting power.
Symptoms
- High intake air temperature at low speed and in traffic that does not fall when the fan should be running
- Reduced power and boost limiting, worst in hot weather or when towing
- No fan noise after a hot shutdown or when the air conditioning is working hard
- MIL on, often with charge air cooler efficiency codes
- Rattling or grinding from the fan area if the bearings have failed
Likely causes
- Seized fan motor or worn bearings, so the blade does not turn despite being supplied
- Debris jammed between the blade and the shroud, or a broken and unbalanced blade
- High resistance in the supply or ground circuit, so the motor gets too little voltage to spin properly
- Burnt relay contacts that pass just enough current to look connected but not enough to run the fan
- Failed fan control module on speed controlled fans
- Intake air temperature sensor reading incorrectly, so the cooling effect is never recognised
- Blocked cooler or radiator face, so airflow produces no useful temperature drop
- Motor worn to the point that it turns only slowly under load
How to fix it
- Command the fan on and physically confirm that it turns and moves air, not just that it is energised
- Measure the current the fan draws while running and compare it with specification; a very low or very high value both point at the motor
- Check voltage at the fan connector with the fan under load and perform a voltage drop test on supply and ground
- Spin the blade by hand with the power off to feel for drag, roughness or contact with the shroud
- Inspect the blade and shroud for debris, damage and missing balance weights
- Verify the intake air temperature sensors read correctly, since a false reading hides real cooling
- Replace the motor or the control module when the tests condemn them, then repeat a hot idle test and confirm the temperature falls