Hello,
This is my first post, but I wanted to pass along some "real-world" experience. I have a 94 Sentra LE (1.6L/MT). Both cooling fans went out at virtually the same time and the Cooling Fan Fusable Link was blown also (the relay may have been cooked as well, but the mechanic(?) got to it first and replaced it with a new one.
I replaced both fan motors with new ones, but this did not fix the problem. Anyway, after the shop tried unseccessfully for days to find the problems, they just wired them to the ignition connection at the relay block. This of course ran the fans, but shorted the ignition and the car would not idle. So I yanked out the "hot-wire" and started to troubleshoot with a meter (I also ran the computer codes to see if I could learn the problem). The computer said I had a bad temp sensor. I replaced it but still no fans (I had 12V on three legs of the Radiator Fan relay, 4th wire goes to the fans). I sweated in the 102* West Texas heat and ready my manual until I was exhausted...
What I found was this: If you grounded the blue wire (on the fan relay), the fans would kick on instantly and run well (the car also would idle correctly). When I broke the connection they stopped. I was performing the computers task and can only surmise that the Electronic Control Module (ECM) is defective (but only on that one circuit). I permanently grounder the blue wire and my fans work anytime the car is running (which in West Texas is probably a good thing). I can detect no "down-side" to this proceedure though I would rather the computer do its job.
If anyone has any insight into this issue, please let me know, ok? I just couldn't see spending $500 for a new ECM.
Sorry this is so long but this took several days!
Thanks for reading,
-Tex