I'm doing some tests on my '88 GTA 5.7 with dual fans.
The driver's side runs constantly with the ignition on. The service manual lists some tests but it is looking more and more like the ecm being bad.
My question is-if the ecm is indeed bad, is it the computer or the prom that tells the fan to run?
Also, if the computer needs to be changed, what would interchange?
And if I have to change the prom, should I go ahead and get an aftermarket version? If so, which one for normal driving with "just a little bit of lunacy"?

 

I'd say start with the relay first. The driver's side should NOT come on until 234 degrees or so and yes it's commanded by the ECM based on a setting in the PROM. It MIGHT be the PROM but most likely (if the rest of the engine functions run properly) it's that relay. On a 92Z28 it's the one closest to the fender among the three relays to the left of the brake booster on the firewall.

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92 Z28 L98 350
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Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

I would check the relay first. Then if things still aren't working properly, I would manually ground the fan sensor, and if that doesn't get it running, manually run power to the fan to see if the motor is burned out.

-EJ

 

Umm... I suggest you re-read his post. The fan STAYS ON all the time. So it is running and the motor isnt burned out.

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92 Z28 L98 350
---------------
Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

I have tried new relays, hoping for a dead short in one of them. No such luck.
I still have to trace the ground wire to the computer but I see no obvious damage-yet.
Looks as if I need to replace either the computer or the prom or perhaps both.
Again, my question is-what runs the driver's side fan---the computer or the prom?
I sure don't want to put in a remanufactured computer (about $95 at AutoZone)just to find out the prom is the culprit, and as you probably know, they don't take electrical items back after installation.

 

JMS,

I remember your previous post (and my long (detailed) answer on how to confirm that the ECM is bad).

To answer your question, only the ECM will need to be replaced (it is probably just a transistor on the ECM that is shorted to ground).

When my ECM went bad (other problem), NAPA wanted about $90 (1999) for a re-manufactured ECM, but got one from GM for about $140 (they liked me (don't know why) so I got a discount).

GM would only guarantee the ECM (60 days or 10K miles if memory serves) if they installed it (about another $50-60). Installed it myself w/o any problems.

BTW, it's really easy to test the ECM as I detailed in my earlier post to you - all you need is a small light bulb with two wires connected to it.

AFTERTHOUGHT: Just thought of an easier way to see if the ECM is causing your left fan to be on continuously. All you have to do is remove the green/white wire at the connector at the ECM (location was given in your first post). With that green/white wire removed from the connector, the fan should be off. Hardest thing about this test will be removing the wire from the connector. You'll have to stick a pin (or other thin hard tool) in the socket (from the socket end - not the wire end) to release a metal tab that is bent out to hold the female pin (socket actually) in the plastic socket. Another (less desirable) way would be to just cut it near the connector (to isolate the ECM only as being bad, just in case something else is shorting it to ground between the connector and the relay) and then solder it back together when done testing.

If you have any more questions, ask.

[This message has been edited by Stuart Moss (edited July 28, 2000).]

 

The PROM doesn't actually energize the relay, it commands a driver in the ECM to energize the relay. And since you can't really corrupt the PROM, chances are the driver in the ECM is shorted.

Also note that if the A/C is on, or the ECM is in "limp home" mode, the fan will always run.

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"I used to have a handle on life, but then I used it as a plunger and broke it" -The Wave

ASE Master Tech + L1
Savannah, GA
'87 Trans Am-K&N,Cold air induction, SSM SFC, Flowmaster, 16" GTA rims.
'97 Bonneville SSE
About Me

 

Thanks guys.
I just checked the C1 (green/white wire and the one the book said to check)terminal at the computer with my test light. With the ignition on, no light on the test light and the fan still ran.
Disconnected the harness at the computer (fan quit running)and probed the wire with the test light which grounded the circuit and the fan began to run again.
I guess its time for a new brain. Mine and the car's!