I am having some problems with the coolant system (Electronic Fans) on my 89 IROC 5.7 tpi. For what ever reason I am getting voltage on E8 from the ECM and of course the fans are not functioning. Everything else checks out on the coolant electrical system except for the above mentioned.

I have removed both connectors from the ECM and retested E8 at the fan relay wiring and there is no longer voltage present on E8.

The only conclusion I can come up with is faulty ECM but what are your thoughts?

 

If you ground the E8 (with the key on), does the fan come on?

 

Not sure there's 12vdc so I don't really want to ground it.

 

If you disconnect the ECM and keep the key off, you should measure around 100 ohms on E8. That's the relay coil. When you turn the key on, the coil is energized and its low side is grounded by E8.
See the diagram:
http://austinthirdgen.org/mkportal/m...ine_wiring.gif

Grounding E8 will actuate the relay and turn on the cooling fan.

Hope this helps.
Lou

 

Yes I understand that, but when probing for voltages on the fan relay connection I am getting 12vdc on E8 from the PCM. This should either be open circuit or closed to ground. Having voltage were a ground should be seems as if it would be a problem?

 

Tried reading my sig?

 

Sweet thanks...

 

On a side note after the vehicle cooled off I was only getting 9.5vdc on E8 at the fan relay wiring connection. So I decided to ground E8, and the fans worked as expected. So is this normal for stray voltage coming from ECM?

 

Sorry, I wasn't clear. I should have said to ground the E8 on the connector with the ECM disconnected. That showed us that the rest of the system works.

Voltage on the ECM side is not necessarily indication of a blown output. Some amplifiers use capacitors on their output to absorb the coil flyback spike.

You can check the ECM output. You can pull the relay and reconnect the ECM. That way, you can turn the ignition on and check the voltage on E8. There should be no voltage there from the relay coil.

Let us know what you find.
Lou

 

Ok I got ya, I will have to work on this this weekend and I will report back.

 

Hey guys new to the third generation world and frankly I'm at my wits end


First of all I have an overheating problem my fans won't come on I have a 89 iroc z with the 305 tpi so far I have replaced the thermostat had the coolant flushed replaced a fan relay and both dual fans and when I turn the ac on the fans still don't turn on the only think I can think of is maybe there's more fan relays that need to be replaced or maybe the fan switch but I have no clue what I'm doin except for what I learned from my 82 to 92 Haynes book but that didn't exactly help either. Any help is more than welcome I could use a pro by my side with this car. Thanks a million

 

Ok I have chased this back to the ecm, I ground ed the relay there with the ECM removed and the fans work. Since this is like the third rebuilt ECM that I have tried I am thinking the Memcal is bad?

 

So what exactly makes you think that the ECM is bad?

 

I have no clue whats wrong I just swapped the ECM this morning so I dont think it could be a faulty ECM. Maybe the Memcal?

 

I do not follow.
You say you have no clue what's wrong but you test your coolant fan circuit and conclude that the ECM is bad.
Why do you think the ECM is faulty and how did you arrive at that conclusion?
What are the actual symptoms?

 

I almost hate to mention this because I am trying to work one problem at a time, but all of my gauges stopped functioning today after about 50 miles driven on the ECM I replaced this morning. Just a FYI in case there might be a link between the two.

 

The ECM is not triggering the relay for the Efans. I removed the ECM and then grounded the relay wire (green with a white stripe) at the ECM harness connection C1 and the fans work. Temp sensor was working last time we checked with the scanner.

 

No link. Gauges in the instrument cluster use a separate set of sensors.
If all gauges went out, I would suggest to look at the GAUGES fuse.

 

How did you test that the ECM is not triggering? IOW, what were the conditions for the test?

 

Because the fans wont come on when the car gets hot.

 

Define "hot". I.e., how high did you go?
And did you verify the engine temperature with anything else besides the scanner? An infrared thermometer pointed at the coolant neck on the top of the intake is a good way.