Engine Coolant Fan not working?

PONTIMAN

MEMBER
1988 BUICK REGAL
2.8L
6 CYL
2WD
AUTOMATIC
18,000 MILES

My engine coolant fan won't work when I'm activating the A/C. It also doesn't work when the Engine is hot.
I jumped 12v to the fan and it starts to turn, so it seemed to be fine. I put in a new fan relay.
I guess the coolant fan switch is bad, and I need to know it's location. Just found one coolant temperature sensor in the thermostat housing, but it seems to be the one for the ECU, not for the fan, or does the fan become it's turn on command by the ECU?
Any ideas are welcome.

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

The coolant sensor that is related to the fan is located behind the thermostat housing.

I attached the wiring schematic for the radiators on this vehicle. I need you to do the following.

First, remove the fan relay and confirm there is power to either pin 30 or pin 87. Those two pins are the secondary side of the relay and one of them gets power at all times from fusible link E.

To determine which connectors are pins 30 and 87, you will need to look at the relay. Each pin will be numbered, the primary are 85 and 86 and the secondary are 30 and 87. Here is a link that explains it much better than me.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know what you find. Note if there is no power to any of the connectors, then we need to check the fusible link.

Let me know what you find.

Take care,

joe

See pics below.

Image (Click to make bigger)

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Wednesday, June 7th, 2023 AT 7:36 PM

PONTIMAN

MEMBER
15 POSTS

Hi Joe,

Many thanks for your reply.

I played around with my multi scan tool today. Here are the results:
Brown plug (coolant temperature sensor for fan).
- grey wire (ground) has continuity to battery ground.
- orange wire has 12 volts reading.

Black plug (coolant temp sensor for ECU)
- black wire (ground) has continuity to battery ground
yellow wire has 5 volts reading (engine cold)

Black plug (to fan motor)
- black/red wire has continuity to relay socket pin 87
- black wire has continuity to relay socket pin 85

Relay socket:
- pin 30 has 12 volts and is all time hot
- pin 85 has 12 volts only if A/C is activated
- pin 86 has no continuity to the sensors or to ground

I also checked the fuses in the glove box and also the fuses under the hood. I cross changed all the fuses and put a new relay for the fan motor in -> nothing changed.

I won't let the car's engine run hot to check if the fan will start to cool it down, so I just check the fan motor working with the A/C.
I guess, the fan motor needs to come on directly with the A/C activated like it happened at any other car I had before.

My next steps will be to find and check the A/C intermediate pressure switch and the electronic control module for continuity.

So, many thanks for the wiring diagram. I'm sure it will guide me to find the issue. I will come back with further results, soon.

Regards,
Heiner

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Thursday, June 8th, 2023 AT 1:32 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

I went through your info. I attached a pic below that is confusing me. Do you mean that pin 85. Wait, I think I understand what you are saying. Ignore me. LOL

As far as pin 86, that will not have continuity to ground until it is commanded by the PCM to turn the fan on. So, to confirm if that is working, you have to allow the engine to reach a higher temperature when it would be commanded on.

Let me know.

Joe

Image (Click to make bigger)