Post by
VStar650CL »
https://forums.nicoclub.com/vstar650cl-u299034.html
Sun Oct 31, 2021 12:46 pm
The fan relay on your ride just provides power to the Fan Controller (FCM). When the fans come on with the key with the A/C off, it either means the FCM has a failure, the PWM driver circuit in the IPDM has a problem, or the ECT sensor has a problem causing the ECM to instruct the IPDM to run the fans. The violet wire into the FCM is the PWM line, it's referenced to 5V with a pullup resistor inside the FCM. The IPDM pulls it to ground with a transistor, 0V is "fan off" and 5V is "max speed". Back-probe the wire and take a voltage measurement when cold, if it's 5V then the fan is doing what it's supposed to do and the problem is elsewhere, probably a bad wire to the IPDM or a blown drive transistor. If it's 0V or 12V then your new Fan Controller is defective. If it's a "middle voltage" then the IPDM or ECT sensor may have a problem causing the fans to run at partial speed all the time, which may be causing your overheats. In that case, let the car get warm and see if the voltage at the Controller rises. If it doesn't then you'll need a scanner with work support to test the fan via software and read the ECT sensor.