I have an 86, which is my driver. The main cooling fan does not run. The fan runs if I feed it 12 volts direct. The aux fan does come on but in stop and go driving it is not enough to keep things cool. I ran all the checks in the service manual and the Haynes manual, and all indicate the ECM is at fault. As I said the fan motor runs but is rather noisy. In the short term I think I will wire the fan with a manual switch by removing the cooling fan relay and inserting leads directly between contacts “A” and “E” with a 15 amp fuse in the line. I think this will work short term but wonder if there is anything else I could check until I replace the ECM. Also for quite some time the fan does not start when the AC is turned on. It only runs when the temperature reached around 2180F - 2220F. Any comments or advice will be greatly appreciated.

Thanks
Ed A

 

When I first bought my 86, I had the very same problem. I located the fan relay (right below the master cylinder on the inner fender well)and removed it only to discover that the silicone or whatever grease they used for corrosion prevention had dried up and was contaminating the fan relay contacts. I used a thin piece of plastic wrapped in 400 grit sandpaper to clean each contact on both sides. Then I used a really small file to sort of bend the contacts closed (sort of a fishmouth affair).
I cleaned the relay contacts with the 400 grit, and the plastic, and reinserted it into the relay socket, and it has worked for 10 years now.
try that, and if it doesn't work, try checking your relay with 12 volts and an ohm meter or just replace it. It's about $11 average at your chevy dealer.
I would check the ECM at the relay socket for coil power with the meter to determine that the ECM is putting out the coil voltage to actuate the relay, and check the relay socket for volts on the main contacts to determine if the 12 volt feed is good. Check for 12 volts with the key ON, but engine off.
after you are done, try this:
Try using a paper clip to the aldl connector under the dash. short A and B (I think) to get the car into the diagnostic mode. When the diagnostics are tripped, the fan is supposed to run in low speed.
If the fan doesn't run after all that, try ohming the wires from the fan relay to the fan, and check the ground wire from the fan.

 

Check the fan relay by grounding its green/white wire with the ign in run. You should hear the relay click closed and the fan should then run or you have a defective fan relay. Check your 3 amp C. Fan fuse with an ohmeter. The ECM turns on the fan relay when the temp sender under the MAF and on the front of the block says the coolant temp is 228 F. You could have a defective temp sender. A scan tool will tell you what the temp sender says the coolant temp is and it should be close to your dash temp gauge. If not, you may have a bad sender or the wiring harness socket is defective that plugs into the temp sender.

 

Thanks for the reply. I ran all the diagnostics in the service manual and replaced the relay. If I short terminals “A” and “B” on the “ALCS” the fan does run. I checked the wire from the relay to the ECM and all is OK. There is 12 volts at terminal “E” of the relay socket. The temperature sensor seems accurate as it blew all the antifreeze out when I was stuck in stop and go traffic on Thursday (the temperature readout stopped at 2990F after I stopped under a bridge in the rain) and was replaced with water which boiled quite nicely at around 2200F while I was testing the new relay on Saturday. All tests indicate the ECM. All grounds are good so do you think removing the relay and hard wiring a fused switch to the fan is a viable short-term solution?

Thanks Ed A

 

So what is the problem? The fan motor works, the fan relay works, the ECT sensor is feeding the ECM, and the ECM turns the fan on as it is supposed to. Is it just the A/C operation? Check the A/C pressure switch.

RACE ON!!!

 

Well the problem is that the main fan never comes on. The car overheats when the engine is on. The auxiliary fan comes on at about 235F but the main fan doesn’t.

 

That comment led to this comment.

 

Not sure on this but I BELIEVE the 86 uses two temp sensors, one for the dash readout and one for the ECM. On my 90, the computer does not use the same temp sensor as the dash gauge (Not even sure if the 86 has the analog gauge). There are two sensors, one for the ECM and one for the dash. Shooting from the lip, if system components work during the test routine, I would try to locate a scanner and take a look at coolant temperature. The scanner will display engine temp the ECM uses. If you don't have access to a scanner, you can remove the temp sensor for the ECM and measure the resistance and compare with Factory Service Manual. (My 90 has a chart).

Also, locate the temp sensor for the ECM and check out the wiring. I've had mine come off during repair.

Seems to me the computer thinks the engine is running cool and is not commanding a good system to come on.

Let us know.

dlmeyers
90 coupe zf6 3 speed shocks

 

GM has a nice selection of fan switches.
238
230
203
and I'm sure many more, but that is what I have found so far.

I think the 230 switch would be a nice replacement for the factory 238.

 

And those switches help with the main fan... HOW???

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depending on the year, the aux switch turns on the main fan via the ECM. So if you put a 203 switch in the head, both fans would come on at 203, without reprogramming.

 

86vetted: When you have time, please complete your profile. If you need help on this task, let us know and we will help you

I read your posting twice to be sure I understand what you are trying to do. You are wanting the ability to manually control the main cooling fan. Assuming the relay is working properly, this is an easy and very cheap modification. All you have to do is locate the main fan wire that goes to the ECM and a schematic will give you this. Create an alternative ground circuit that goes through a switch mounted under your dash. Turning on this switch will make the fan run regardless of the ECM programming. A word of caution - once you turn on the fan.....it runs until you turn if off. If the ECM controlls the fan, it shuts off the fan at speeds above 35 MPH.

I have done this to my 89 and can send photos of the switch and ground wire location.

 

No! No! No! That is totally wrong. Unless it was rewired, the aux fan and the main fan have NO interaction with one another. The auxiliary fan, aux fan relay and aux fan switch, is a 100% stand alone system. The ECM never knows if or when the aux fan is running. There is no aux fan feed back to the computer. With hoobledy doodledy like this being passed off as advice, it is no wonder there are so many misconceptions flying around this forum. Get it straight in your own head before passing garbage on to those wanting to learn.

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I here at the shop, and looking at an 89 F-body manual. (no y-body manuals here....) Looking at the 89 F body 350 TPI motor, which is the same but with iron heads...... dual fans.

The A/C presure switch, and the aux cooling fan switch are wired back to the ECM. If either of them ground out, so does the ECM, which involks the primary fan.

I have to dig up an early Y manual to see if it is the same.

 

It ain't

http://members.shaw.ca/corvette86/Co...%20Control.pdf

 

The only thing remotely close to what you're saying is the "aux fan switch" in 85 turns on the main fan for non-Z51 cars at 238F. But this switch does not go to the ECM.

 

ok, so excuse me for getting my Y and F mixed up.

 

86vetted, ECM is rarely the cause. What you really need to check is your Coolant Temp Sending Unit.

It's located on the front of the intake baseplate and has a plug with a plastic clip. (Not to be confused with the cold start sensor switch next to it with a metal clip.)

The ECM turns on the main fan when this sensor reads 228F. It also uses it to control fuel mixture, and some other things.

If this sensor is reading low the main fan will come on late or not at all. You would have to use an ohm meter to read what it's telling the ECM, and find the chart that says what it's supposed to read. The reading on the dash is from a different sensor.

You could also try unplugging it and seeing if the ECM throws a code. It might even turn on the fan if it can't read the sensor, I don't know.

The ECM also uses vehicle speed to control the main fan, but I assume your speedo works.

 

You didn't get em mixed up. You looked up what the F-body wiring was and assumed the vette was the same. Just keep in mind that a few guesses here purported as fact can lead to a guy spending hapless hours diagnosing and replacing parts that are fine. I've been that guy. I'd rather have no information than wrong information.

 

What you neglected to say was that the non-Z51 cars you refer to have no aux fan. Therefore the thermal switch in the right head of the non-Z51, 1985, isn't an auxiliary fan switch. That switch in the single fan '85s, is merely a back up to the ECM activation.



Not in cars before 1990.




There is a lot of that flying around these days.

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