What does it mean?
Modern output stages are intelligent: they measure the current they are passing, the voltage on the line and their own temperature, and report back whether the result matches the command. This code is stored when that self-check fails on the charge air cooler cooling fan output, without the line being clearly high or clearly low.
In practice the driver is telling the software that the load it is switching does not behave the way it should: too much current, a state that does not follow the command, or an output stage running too hot to keep switching safely. It sits between a simple wiring fault and a fan performance fault, so the diagnosis has to look at the load, the connections and the module supply together. The output is usually disabled to protect the driver, leaving the fan out of action.
Symptoms
- Fan not running, or running only briefly before it is switched off again
- MIL on with the fault reappearing after each attempt to operate the fan
- Intake air temperature rising in traffic and reduced power under load
- Fan noise or vibration when it does run, indicating a struggling motor
- Occasional blown fuse in the fan supply circuit
Likely causes
- Fan motor drawing excessive current because of worn bearings or a partly shorted winding
- High resistance in the supply or ground path making the driver work outside its normal range
- Corroded or loose terminals in the fan or module connector, which heat up in use
- Incorrect replacement fan with a higher current draw than the original
- Poor module ground, so the output stage cannot dissipate heat properly
- Water intrusion into the module connector causing leakage between pins
- Blade jammed by debris, which forces a stall current through the driver
- Internal damage to the output driver after a previous short circuit
How to fix it
- Command the fan and measure its current draw with a clamp meter, comparing it against specification
- Turn the blade by hand with the power off to feel for bearing drag, and check for debris in the shroud
- Perform voltage drop tests on both the supply and the ground while the fan is running
- Inspect the fan and module connectors for heat discolouration, corrosion and loose terminals
- Clean and tighten the module ground points and check for water intrusion in the connector
- Confirm the fitted fan is the correct part for the vehicle, since a higher current unit will overload the driver
- Replace the fan when it is proven to draw too much current, and consider the control module only after the load and the circuits are proven good