Cooling fans are not working on my car?

CAT4690

MEMBER
1999 CADILLAC DEVILLE
V8
FWD
AUTOMATIC
107,000 MILES

My cooling fans are not working on my car, I hooked up my fans directly to my battery to check the motor and the motors are good. Idk what else it could be or how to fix it. Also I went to advanced auto parts and had my engine diagnosed and I had a code of P1660 it said Factory Controlled Auxiliary Input/ Auxiliary Output. But that could be anything? Does anyone know what it means exactly?

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

Cooling fan can be inoperative typically for having faulty relay, coolant temperature sensor or the fan motor.
Since you verified that the motor is good you need to check the relays.
This vehicle has 3 cooling fan relays. They are located right behind the cooling fans (see diagram below).
The relays can be tested to see if they are indeed bad:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Another item to check would be the coolant temperature sensor. The sensor sends the signal of when to start the fans.

https://www.2carpros.com/articles/how-an-electric-cooling-fan-works
https://www.2carpros.com/articles/replace-electric-fan-motor

I have attached the coolant temp sensor location as well as replacement procedure for your reference. Also attached the wiring diagram.

Please let me know of any questions.

Thank you.

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