Cooling fan wiring diagrams for fans they do not engage properly

LMFITZ

MEMBER
1998 CHEVROLET LUMINA
6 CYL
FWD
AUTOMATIC
566,756 MILES

Diagrams for fans they do not engage properly. The water pump was recently changed. Now the fans will only work in any ac mode. So it overheats in traffic or idling sitting still. With Texas summer coming I need to get this fixed. I have swapped 1 and 3 relays to others in the system I tried to operate in ac mode without the #2 fan relay installed no work. Reinstalled and it works in ac modes. When I pulled the 60A maxi fuse (Center, IGN SYST Relay, WCMPT REL Fuse, PCM BAT Fuse) next to the fan 1 30a maxi fuse the #1 fan kicks on but engine stalls. Checked for latent engine codes nothing. So I m currently thinking PCM. Or BCM.

Sunday, November 8th, 2009 AT 1:14 PM

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

I would think you are correct. However, let's confirm this by checking to see if the PCM is grounding the relays.

Let's do this by putting your red meter lead on the battery positive and the black lead on the wire on the PCM for the relay control. Start the engine and when the fan is to come on, the PCM should ground this wire and the meter will show 12 volts. Does that make sense?

https://www.2carpros.com/articles/how-to-check-wiring

Below is a wiring diagram for this. If the PCM does not ground the relay to turn the fan on then the PCM is the issue.

Image (Click to make bigger)

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Monday, March 15th, 2021 AT 12:36 PM

CHRIS LAUCH

MEMBER
1 POST

That’s exactly what happens. Also if I manually ground the relay it turns that fan on.

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Monday, March 15th, 2021 AT 5:11 PM

KASEKENNY

MECHANIC
18,907 POSTS

If you are grounding the relay and it works then that makes even more sense because the PCM is what grounds the relay to close it. So by grounding it, you are taking the place of the PCM and doing its job for it.

If it were me, I would replace the PCM based on this info.

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Tuesday, March 16th, 2021 AT 5:38 PM