Cooling fan comes on when retrieving codes!?!?!?

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May 27, 2006 | 05:26 PM

VtVette

Thread Starter

Melting Slicks

Joined: Mar 1999

Posts: 2,830

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From: Las Vegas Nevada

Cooling fan comes on when retrieving codes!?!?!?

I was diagnosing an issue where my cooling fan comes on whenever the engine is running. Not when the ignition is on, only when the engine is running. I figured I would check the ECU for codes so I jumped the terminals in the ALDL connector with the paper clip. When I turned on the ignition with the paper clip in place the cooling fan came on. I do not know enough about the diagnostic mode of the ECU to know what this means. Can someone elaborate for me?

thanks,

May 27, 2006 | 05:35 PM

aboatguy

Race Director

Joined: Jan 2005

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From: Slidell Louisiana

When I retrieve codes or program my ECM the fans come cycle on for a second or two.

Mike

May 27, 2006 | 05:46 PM

VtVette

Thread Starter

Melting Slicks

Joined: Mar 1999

Posts: 2,830

Likes: 20

From: Las Vegas Nevada

I've never seen this happen before. The main fan was on the whole time I was retreiving codes. I've got to believe this has to do with my fan being on whenever the engine is running.

May 27, 2006 | 05:49 PM

CFI-EFI

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Joined: Sep 2000

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From: The Top of Utah

It is supposed to. The IAC will also close, and most solenoids and relays will be activated in the diagnostic mode. You won't find any codes that will lead to the diagnosis of that fan problem. Do you have an auxiliary fan? The 1985 without an aux fan uses unique circuitry. Your problem may be the result of your cross breeding the car and the wiring harness.

RACE ON!!!

May 27, 2006 | 06:05 PM

VtVette

Thread Starter

Melting Slicks

Joined: Mar 1999

Posts: 2,830

Likes: 20

From: Las Vegas Nevada

Quote:

Originally Posted by CFI-EFI

Thanks for the info CFI. The car had an aux fan, and the '86 harness has all the wiring for the aux fan.

The cooling fan circuit is pretty basic, and it's been covered here on the forum before. Unfortunatley my '86 manual does not have the diagnostic flow charts, it's a white cover edition. I do have the wiring diagrams though. I'm sure I will figure out what is triggering the relay. I was just startled when the cooling fan came on. I wanted to make sure this was not some sign of a faulty ECU.

thanks guys,

May 27, 2006 | 06:21 PM

RRT vette

Le Mans Master

Joined: Feb 2006

Posts: 8,753

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From: Louisiana

Quote:

Originally Posted by CFI-EFI

My fan on my 86 comes on and stays on the whole time I run the ECM diagnositic check. Normal, I would assume.

May 27, 2006 | 06:44 PM

Steel Breeze

Burning Brakes

Joined: May 2006

Posts: 1,097

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From: Richfield Utah

Quote:

Originally Posted by RRT vette

My fan on my 86 comes on and stays on the whole time I run the ECM diagnositic check. Normal, I would assume.

What He said...

May 27, 2006 | 08:55 PM

CFI-EFI

Race Director

Joined: Sep 2000

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From: The Top of Utah

Quote:

Originally Posted by VtVette

The cooling fan circuit is pretty basic, and it's been covered here on the forum before. Unfortunatley my '86 manual does not have the diagnostic flow charts, it's a white cover edition.

I don't know that any FSM has a trouble shooting chart for the fan(s). As you stated, it is a pretty basic relay powered system. Since your 1985 came with the aux fan, the 1986 harness for an aux fan should work just fine. The ECM causes the primary circuit of the relay to close when the ECT sensor signals the ECM that the engine has reached the temp programmed into the prom for fan activation, or the A/C pressure switch indicates to the ECM that the A/C is on. A bare wire in circuit# 335 could cause a ground that would close the relay and cause the fan to run.

RACE ON!!!