Cooling fans are not working, overheating when idling

Tiny
ZACH MUSICK
  • MEMBER
  • 2001 BUICK CENTURY
  • 3.1L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 144,000 MILES
Okay, I have been on a journey. This might be kind of long.

So, this is what I've done:

Replaced radiator, radiator cap, cooling fans thermostat, heater core, water pump, coolant temperature sensor.

After replacing all of that, the cooling fans would kick only when I turned the A/C on. Or so I thought. Turns out they were functioning normally but not at the correct temperature. Low speed would turn on when the needle reached the just before the 3/4th temperature gauge line. High speed would turn on at the 3/4th temperature gauge line. So, I figured the PCM must be faulty. (Among other tall tale signs)

So, I replaced the PCM. Fixed a lot of issues. But ended up going back to square one. Cooling fans won't come on. Not even for ac this time. So, I broke the trustee multi meter out and started rechecking wiring. Bringing me back here today. Now, the cooling fan 1 relay is not getting properly powered. According to my relay. Post 85 and 86 should have 12 volts power, and post 30 and 87 should have no power until tripped. Well, 86 has 12vs 85 has no volts 87 has 12 volts. And 30 has no volts.

So, I'm assuming 85 and 87 have crossed somewhere and that I'm needing a wiring diagram.
Wednesday, June 1st, 2022 AT 11:15 AM

3 Replies

Tiny
ZACH MUSICK
  • MEMBER
  • 4 POSTS
Here's a picture of what's going on.
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Wednesday, June 1st, 2022 AT 4:05 PM
Tiny
ZACH MUSICK
  • MEMBER
  • 4 POSTS
Okay. So, I already know it's a wiring issue. But it is now throwing codes for the fan relay 1 and fan relay 2.
Codes po480 and po481.
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Wednesday, June 1st, 2022 AT 8:07 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
You may be correct that this is a wiring issue, but we need to start with making sure you are getting the correct voltage.

I am attaching the picture of the relay below. This will have the diagram of the layout on the side of it so let's make sure we are getting the proper voltage on these pins.

You should have voltage on pin 85 and 87 at all times. 86 is the ground from the PCM so if you are checking for the voltage on 86 you need to remove the relay and supply voltage and use 86 as the ground.

If the meter says 12 volts, then the PCM is grounding the relay to command it on.

As for 30, that is only going to have voltage when the relay is grounded and it closes. To check the operation of the fan, jump power to 30 from 85 or 87. The fan should come on.

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

However, I am attaching the testing as well for these codes because that will help walk through this testing.
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Thursday, June 2nd, 2022 AT 8:41 AM

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