1985 Cooling Fan diagnostic help.
Thread Starter
1st Gear
Joined: Sep 2023
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1985 Cooling Fan diagnostic help.
Hello all. A little technical help would be appreciated. 1985 L98, bone stock. Having issues with the main cooling fan. P/O had the fan relay wired up to a toggle switch due to what looks like a melted connector. Removed the toggle switch, wired in a replacement relay connector. Put in a new relay, and no dice. Let the car hit 240 at idle and the cooling fan didn't kick on so I shut it off and started to diagnose. With NO relay and the red and black wires jumpered at the connector the fan kicks on, but with relay installed, A and B on the ALDL jumpered and the key on no dice. From what I've been reading, the Coolant Temperature Sensor could be the culprit. But I'm unsure. The 3amp fuse at the box is fine, the fusible link on the red wire to the fan relay should be fine since when I jumpered the connector the fan worked. And I have 3 different brand new fan relays so they can't all be duds. Any advice is much appreciated.
Drifting
Joined: Aug 2022
Posts: 1,509
Likes: 429
From: Ruskin, FL
Hello all. A little technical help would be appreciated. 1985 L98, bone stock. Having issues with the main cooling fan. P/O had the fan relay wired up to a toggle switch due to what looks like a melted connector. Removed the toggle switch, wired in a replacement relay connector. Put in a new relay, and no dice. Let the car hit 240 at idle and the cooling fan didn't kick on so I shut it off and started to diagnose. With NO relay and the red and black wires jumpered at the connector the fan kicks on, but with relay installed, A and B on the ALDL jumpered and the key on no dice. From what I've been reading, the Coolant Temperature Sensor could be the culprit. But I'm unsure. The 3amp fuse at the box is fine, the fusible link on the red wire to the fan relay should be fine since when I jumpered the connector the fan worked. And I have 3 different brand new fan relays so they can't all be duds. Any advice is much appreciated.
Drifting
Joined: Mar 2006
Posts: 1,263
Likes: 188
From: Wabasha Mn
Hello all. A little technical help would be appreciated. 1985 L98, bone stock. Having issues with the main cooling fan. P/O had the fan relay wired up to a toggle switch due to what looks like a melted connector. Removed the toggle switch, wired in a replacement relay connector. Put in a new relay, and no dice. Let the car hit 240 at idle and the cooling fan didn't kick on so I shut it off and started to diagnose. With NO relay and the red and black wires jumpered at the connector the fan kicks on, but with relay installed, A and B on the ALDL jumpered and the key on no dice. From what I've been reading, the Coolant Temperature Sensor could be the culprit. But I'm unsure. The 3amp fuse at the box is fine, the fusible link on the red wire to the fan relay should be fine since when I jumpered the connector the fan worked. And I have 3 different brand new fan relays so they can't all be duds. Any advice is much appreciated.
Drifting
Joined: Jul 2022
Posts: 1,805
Likes: 365
From: Central Florida
I might have a question on this as I do not have an 85, shouldn't the jumper on the ALDL overide the temp sensor ?? That would be the ECM directly commanding the relay right ?? Maybe test the fan itself to see if it is working. Another would be to check the command from the ECM to the relay. The last would be to check the ground and also power from ignition at relay. Could the P/O's switch be to fix a failure ?? Possibly an ECM or fusible link failure.
Is speedometer , range etc working correctly ?
Below you will see (on an 86) the relay is activated (closed) by the ECM-ground and the ignition 12v+.
Once the relay is closed the fan power is routed from the fusible link, the fan also needs it's ground.
.
.
Is speedometer , range etc working correctly ?
Below you will see (on an 86) the relay is activated (closed) by the ECM-ground and the ignition 12v+.
Once the relay is closed the fan power is routed from the fusible link, the fan also needs it's ground.
.
.
Last edited by Vets-Vet; May 24, 2024 at 11:15 AM.
Melting Slicks
Joined: Nov 2016
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From: So Cal
2023 C4 of the Year Finalist - Unmodified
Another test: With the engine running, but coolant temperature below fan turn-on temperature, disconnect the CTS. There should be an immediate Code 15 (CTS voltage high), and the fan should turn on by default. Does it?
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
When the CTS on my 84 failed the temperature was all over the place and the car burned 10 gallons of gas in ten miles, literally.
Just now my cooling fan is giving me a problem. I pulled the wire from the switch, drivers side of engine and ground it. The relay is clicking but the fan is not spinning. I ran power to the fan motor and it runs. Up to this point the fan was coming on at 210/215. I really hate running the toggle switch. If I jumper the coolant temperature switch. Should the fan run? Thank you
Oh and thank you to all our veterans
Just now my cooling fan is giving me a problem. I pulled the wire from the switch, drivers side of engine and ground it. The relay is clicking but the fan is not spinning. I ran power to the fan motor and it runs. Up to this point the fan was coming on at 210/215. I really hate running the toggle switch. If I jumper the coolant temperature switch. Should the fan run? Thank you
Oh and thank you to all our veterans
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Racer
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From: Langton, Ontario, Canada
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It's easy to check the wiring of the main fan. Just touch the wire going to the temperature switch to ground, and the fan should come on when the ignition switch is on. Start there.
Melting Slicks
Joined: Nov 2016
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From: So Cal
2023 C4 of the Year Finalist - Unmodified
After his first post, the OP hasn't been back for a week. He probably won't be either. His initial post indicates he knows how the circuit functions and that he suspects wiring issues at the relay connector. He knows that jumping A&B should cause the fan to run and it doesn't. He probably figured it out on his own, and has it fixed.