Hello, thank you for choosing Just Answer. My name is XXXXX XXXXX X will help with your cooling fans not coming on.

It sounds like you have done some good testing so far. We know the fans are good, the relay is good, and the wiring from the relay to the fans is good as well. The only other likely culprits are your ECM or coolant temp sensor.

On your Altima, the temp sensor is the same part as the temperature gauge sending unit. The ECM reads inputs from the speed sensor, temp sensor, camshaft sensor, and A/C controls. From there it sends the signal for to the relay to turn on the fan(s). The fan switch/temp sender unit is less than $20. It is worth a try replacing it. However, if that does not solve the problem, your ECM is likely the failed part.

I hope my answer is helpful. Let me know if you have any additional questions.

Best Regards,
Stephen

Clock going off when you step on the brakes sounds like a bad ground (somewhere). The ECM is located under the dash, in the center of the car, below the A/C controls. You can access it from the passenger side or driver side.

The '97 ECM won't work. In 1996 the engine controls went from OBD1 to OBD2. You would need a '93-'95 with the same part number on the case.

You can try to trace wires back from the signal to the solenoid to the ECM harness, you can do this with a multimeter. But, that will only tell you if the wiring is good between the ECM and relay (99% chance it is fine). You could test the ECM by checking for a signal to the fan relay when the engine is warm enough to turn on the fan, or with the A/C on.

There are a dozen or more ECMs for your car on E-bay ranging from $40 to $150. I'm sure one of them matches the numbers on yours. Make no mistake, this is more than a hunch. Every other possibility has been ruled out. Were it my car, based on what you have told me, I would replace the ECM.