Check Engine light GONE! Fans STILL run all of the time

[davew833]

Today, in my ongoing quest to figure out why both my cooling fans run all of the time, I bought a brand new temp sensor (the one with the two-pin connector) which I installed, and then attempted to clear/check the ECU codes. After connecting the blue wire(s) in the proper way and turning the key, I got NOTHING, no 'check engine' light at all.

Further investigation showed the 'check engine' light didn't EVER come on at when I turned the key. I figured the bulb must be bad. Upon closer examination, I noticed half the screws were missing out of the instrument cluster trim panel. I removed the rest of the screws, and removed the instrument cluster itself to find that the 'check engine' light was GONE! The bulb, the housing, the whole thing!

Knowing that my car passed through the hands of four or five used car dealers before it ended up at the auction where I bought it (with a bad front diff), the missing bulb is a good example of what some unscrupulous used car dealers and/or repair shops will do to pass off a car as being in top running condition. (For all I know, the odometer was rolled back too when they had the instrument cluster out!) The moral of the story is CAVEAT EMPTOR, or specifically, ALWAYS make sure the 'check engine' light comes on (and goes off) when you start that car up you're looking to buy.

The good(?) news is that I replaced the 'check engine' light assembly, checked/cleared the codes, and the light blinked regularly to indicate there were no error codes, BUT MY FANS STILL RUN ALL OF THE TIME! (sigh...) Does anyone know WHICH TEMP SENSOR activates the cooling fans? Maybe it's the other one that's bad. (The dash temp gauge works, though.)

[dwd1985]

I had a problem similar to this, but kind of the opposite. My engine cooling fans wouldnt ever go on, at any time. I tried replacing the sensor, and that didnt do anything, so what we figured out was if we disconnect the wire to the sensor, the fans would run all of the time, and the CEL would turn on. But as soon as I plugged the wire back into the sensor, the fans would go right off. So I looked in the fuse box under the hood, and found the relays, and messed with them for awhile, and eventually got one of the fans to go on, and realized I had some bad relays. I bought a couple from a local Subaru dealership ($45 a piece), and it fixed the problem, and it hasnt come back. So what im thinking is, you either have a bad connecting wire to your temperature sensor (and it thinks it is unplugged all the time because its not reading), or you need to mess with your relays for awhile, and see if maybe you have some bad ones.

[Earthworm]

Sounds more like a relay than the sensor according to the previous explanation since he doesn't get any codes.

You did put a bulb in right? I would have used one of the shift indicator lights until I could purchase a replacement.

Originally Posted by davew833

Does anyone know WHICH TEMP SENSOR activates the cooling fans? Maybe it's the other one that's bad. (The dash temp gauge works, though.)

The sensor you replaced is used by the ECU to turn on the fans and to help with cold starts. The other sensor operates the guage. I'm with Earthworm: it sounds like a stuck relay.....or some one rigged the fans to run all the time to hide an overheating problem.



Dave

[TomsSVX]

I have a full fuse box from under the hood... If you need a relay just shoot me a pm

Tom

[Electrophil]

Originally Posted by Earthworm

Sounds more like a relay than the sensor according to the previous explanation since he doesn't get any codes.

You did put a bulb in right? I would have used one of the shift indicator lights until I could purchase a replacement.

David has it dead on. The relays in question have their springs set up to be normally closed. A "normally bad" relay in this configuration would have your fans run continuously. By normally bad, I mean the relay's coil opened vice a broken spring inside the relay.

[Earthworm]

I believe he answered this in another thread where he found that someone had jumped the connections on the relay with a wire and without the jump the fans did not come on at all.