Well, if the light comes on, it means that the ECM can't talk to the FCM.
What I mean is:

• IF the FCM has lost contact with the ECM (that would mean the ECM has also lost contact with the FCM) and the ECM will light the light.
• If the FCM has lost contract with the ECM the FCM will run the fan at full speed (emergency mode).

Since you have no light, either the FCM has nutted up in such a way that it is talking to the ECM but not running the fan properly or the FCM is fine and the ECM is telling the fan to run for some reason.

So, is the fan running FULL SPEED? That is, can you hear it running from 100 feet away from the car? (It is NOISY when running full tilt). If so, I'd say the FCM is flaky. If it is running at some moderate speed, then the ECM is probably telling it to, but why I don't know.


Keep in mind the fan runs at about 10-15% speed if the A/C is on in the car, to provide condenser airflow when the car is not moving. This is absolutely normal.