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Engine fans

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digitalgpbandit

New member
I’m having an issue with my ‘99 Grand Prix to where it’s getting to the point of overheating when I have the ac on while either stopped or idling or at low speed driving. I initially thought it was the water pump until today it started happening. I pulled over in a church parking lot popped the hood and noticed only the driver side fan running. It didn’t even seem to be going full speed either. This was with the ac on and the temp gauge 3/4 of the way up. Both fans should have been running full speed. I shut it down and let it cool off for a bit. Started driving again, but left the ac off. Made it home and the gauge never went over half way. I popped the hood with it still running when I got home and noticed both fans were running now.

I am a bit nervous now with this 90 degree weather. I do have safeguards (if you call them that) such as a 180 degree tstat and dhp pcm which turns on the fans at the lower temp and keeps them running low speed for a minute after engine shut down. I also did a coolant flush about two months ago on it.

Are there any known issues with the engine fans I should be looking out for? What would cause only 1 to run?
 


temp sensors fail, or its little harness can fail. the relays fail too.

have you made sure the coolant is full since the flush?

if you unplug the temp sensor both fans should turn on full speed. thats a safeguard lol
 
I literally just had the same problem.. ended up being the relay.. only did it when the ac was on and when temp got to 195.. weird

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I topped off the coolant the other morning as it was a little under the cold line. Made no difference. Good to know about unplugging the sensor. Will that knock out my gauge too or does that read off a separate sensor?

I did not see any breaks in the wiring or exposed wiring that would cause a short. Between the temp sensor or to the fan. The loom going to the temp sensor is cracked and brittle but the wires still appear good.

I experimented earlier with the relays. With it running and ac on both fans were working this morning. Relay #10 I unplugged and it shut down both fans. I plugged it back in and both fans kicked on again. I then did the same with relay #12 and it shut down the passenger side fan only, however when I plugged it back in the passenger fan still stayed off. I didn’t do relay #9. I’m thinking #12 May be my issue. For $6 I think I can take a chance on it as I don’t have a working volt meter with me
 
I started having issues again the other day and noticed the passenger fan wasn’t running again when I popped the hood. I happened to touch the harness on the top side of the fan assemly and it kicked on. Then I moved it and the fan went off again then wiggled it again and the fan came back. The driver side fan ran completely unaffected. I am narrowing it down, but with a 90+ degree day and an engine heated over 220+ degrees it was just too hot to further investigate


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Came across my old thread. In any case I replaced the harness going into both fan motors with a used one I located and both fans have been working flawlessly since. For now she is in hibernation for the winter
 


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