I know this topic has been posted many times, I've read them all and am still stuck.

89 Corvette, primary cooling fan is not coming on. No codes being thrown. Aux comes on right around 238 so aux seems ok.

I jumped the ALCL AB and the primary came on. So I'm thinking either ECM or sensor or wire in that circuit. For 7.99 and a quick change I yanked the sensor and replaced it. (the sensor at the front of the intake, in my car the right side 6-8 sensor goes to the dash, the left 1-3 goes to the aux, and the one in front goes to the ECM) Fan still not coming on. If it was open or short to the sensor, I would think it would throw a code, but no code, so I'm thinking wire from sensor to ECM is good.

Other option is wire from ECM to relay. I'm not sure exactly how the AB jump works but I'm guessing that it just goes back to the ECM and the fan is actually firing from the ECM, not any kind of by-pass, so it seems that is good.

Just for kicks I unplugged the 2 connectors to the ECM and replugged them back in. They looked clean and fit snug.

ECM is having no other issues that I can detect, would it be likely to fail on just the fan? Have I narrowed the problem to the ECM? Anyway to validate?

Thanks for any help.

 

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

 

Here's what I found:

The 86-89 main cooling fan is controlled by the ECM. If the car is equipped with an optional auxiliary cooling fan, which is option B4P, the fan is controlled by a brass cooling fan switch that is located on the driver's side cylinder head between spark plugs 1 and 3.

The one in the front of the intake manifold is the coolant temp sensor that the ECM uses to calculate timing and injector timing. On pre 89 Vettes, there's a second switch right next to it in the front of the intake which sends the coolant temp to control the 9th cold start injector on-time.

Jake

 

Best to troubleshoot with a scanner. Spec is 226 degrees for the main fan (228 for the aux). You will only get a trouble code if it's open (-32 degrees) or shorted (306 degrees) and you generally don't have a partial open or short - it either is or it isn't. Mine was intermittently toggling between 220 & 250 which led to hard cold starts. You may have the opposite situation: Is it difficult to start hot? Is the idle too high? Circuitry was good as was the sensor so a new ECM fixed it. Other '89 owners have posted similar problems in the Scan & Tune Section.

 

When you jumper ALDL pins A&B and turn on ignition the ECM should bring on the fan (similarly if you open the A/C pressure connector and start the engine) so the connections between ECM-relay-fan are OK.

This only leaves the wiring from the coolant temp sensor (in the intake base) to the ECM, since you have a new sensor installed.

As suggested, a scan tool would tell you for sure if the ECM is seeing the correct temp, though I think it is not.

 

Since his engine is an 89 and has the aux cooling fan, according to the information I have, his main fan is controlled by the switch in the driver's side cylinder head between 1 and 3, just as mine is on the 86, not anything in the intake.

Maybe on engines that DON'T have the aux fan the main fan switch is in the intake manifold, but I don't have any info on that setup to know for sure.

What am I missing here?

Jake

 

Switch in drivers side head is for aux fan only

 

I purchased a temp switch on 200 off 185 with the two wires, wired mine up so both main and aux come on at the same time-I made no changes or reprogramming to the ECM. I think 65Z01 has a write up on his site how to accomplish this.Ecklers sells the switch for $39.99
page 84 in the 2005 C4 catalog NO. 4205." The switches will turn on the main fan, auxillary fan or both at a lower temperature." With directions.

I only took the quote from the catalog because when I've stated this before -well another story.All I can say is it sure works great for this happy camper.

 

Jake, my '88 is wired like the '89:
-aux fan switch - between #1 & #3
-gauge temp sensor - between #6 & #8
-ECM temp sensor - in intake base, below the TB, just right of center

Rick, actually I put that wright up into a C4 Tech Tip. It's a simple mod and only costs a few $$ in parts at Radio Shack.

 

I bought just the switch because my 86 has the b4p option. (200/185)
With my old switch (between 1-3) the main fan came on at about 225.
I installed the new switch and the only fan that comes on is my aux. fan. The strange thing is, is that the aux. fan comes on a 185/187 and stays on. I even tried another new switch 200/185 and it does the same thing. If I put the old back in, everything is back to normal. I guess I need to rewire something to make it work? on at 200 off at 185.

 

Are you sure you got the right switch (the one with two wires)? look at what 65Z01 said above-tech tip.Go to the top and click on "other", then click on C4 tech tips, 65Z01 has a very inexpensive, easy to follow write up on it.

 

I order it from Mid America and told them about the problem, and they sent me another one at no charge. Its the switch between #1 and #3 on the drivers side head. Yes I just looked at the tech tip from 65Z01 and when I get time I will try that. Unless they sent me two that are wrong, its just strange that it does that.

 

So I had put my original post in yesterday afternoon about the fan, didn't get any replies in for a while and had some other things to do so I decided to put the car away for the night (I live in the city and park in a garage a couple blocks away).

Now keep in mind that I had been screwing around on and off all day trying to narrow down the problem and had been running it up to temp, shut down, fiddle around, run it up, run down for a part ... no problems at all except for the fan issue.

So last night I go to put it away .... total meltdown, the f'er would barely start, had to keep the revs high to keep it running, take the foot off the gas and she would die right away, running rough. F me. No codes set. I pulled the negative terminal off to reset the ECM anyway. Gave it 1/2 hour, same ****. Nursed it to the garage and left it for today.

Went down and 1st thing checked for codes, nothing (fan kicking on no problem with the jumper in though). Figured I'd try a reset again for kicks. Tried to start, same ****. Happened to hear an odd noise in the left front area when the ignition key was on, narrowed it to the fuel cannister solenoid buzzing. I read up and that can cause a rough idle so I yanked it and manually plugged the air line to the intake to check it out. Try to start, better but still won't idle, running rough and I have to gas it to keep it running.

I can see the possibilty of the solenoid going, but multiple components suddenly simultaneously failing? I'm going for a new ECM. Unfortunately I can't get to it til next Friday (travel) but I'll post how I make out.

By the way, back to the original problem, thanks for all the info, especially the diagnostic pdf (I got to get a service manual). Unfortunately with this other 'issue' I can't finish that problem. My guess is that it is the ECM on that problem as well.

FYI, sensors and switches are definitely as orginally posted (the right side 6-8 sensor goes to the dash, the left 1-3 goes to the aux, and the one in front goes to the ECM).

 

Okay guys, I think I've got it now.

I went back to find where it was I got the info I posted earlier. I found it in the Corvette Central catalog 4D, page 41.

But, after checing the Shop Manual for the 86, I see that the sensor in the front of the intake manifold also allows the ECM to control the fan.

So, the temperature readings that the ECM receives from that sensor is used to control the on/off of the main fan.

Have I got it right now?

Now, I'm thinking that since I have an aftermarket aux fan (factory one threw a blade) AND a Derale oil cooler that has it's own fan, I could tie them into the main fan relay used by the ECM. Then those two fans would operate automatically by the ECM rather than the toggle switch arrangement I'm currently using.

I believe that relay is on the driver's side radiator shroud, am I at least right on that?

Ponder, ponder, ponder .

Jake

 

Jake, sounds like you're on the right track-yes the main fan is operated by information the ECM receives from the sensor on the front of the manifold.At least on an 87 there is a main fan relay located in front of the battery on the wheel well. The temp switch for the aux fan is located between #1 and #3 drivers side-should be a single green wire or green and white wire (can't remember-at work). The aux fan relay is the one on the radiator drivers side.Now if you go to "other" at the top of the page and click on it-then tech tips you can find 65Z01 article on fans.I think I would read thru it carefully and try this first before going the other route w/aux fan and cooler. If you haven't got a Helms manual-there invaluable-for the wiring diagrams etc. the Haynes has them to but there hard(at least for me) to read because of size.Agent 86 has been posting wiring diagrams etc. so if you haven't got one-you might try paging him.

Once again-I think you have it pretty much right now.
Good Luck

 

My 86 fan relay's are located in the same spot as your 87. Aux. by the radiator and main on the wheel well by the battery. I have one green and white wire going to the aux. fan switch. I'm going to try the jumper wire next weekend.

 

I have been having problems with my fan also. I have not seen anything like it in the search results.
My fan motor burnt out and took the fusible link with it. I have an 88 with the auxiliary cooling fan. I replaced the motor and both links with fuses. I replaced the thermostat also. I checked both relays and checked the display temp sensor and the switch for the auxiliary cooling fan. My main cooling fan is coming on at 150. I the replaced the temp sensor for the ECM. It is still coming on at 150. Any ideas?
I am going to see if the fan stops when the car moves at over 40mph like it should. An am going to wire a small 12v light on to the fan side of the relay and se if the light goes off.

If I have to replace the ECM, is it just the EPROM or the box or both?
Thanks Bill.

 

One thought is that your dash is displaying the wrong temp? How are you measuring that 150 temp? You say you checked the display temp sensor (single wire, blade connector, between 6&8 right side), how did you do that, did you measure resistance at varying temperatures?

 

No. I just unplugged and cleaned the connection. The motor comes to 150 pretty quick. Outside temp is about 45. If I let it idle it will come up to about 210.
I don’t recall seeing the resistance values in the shop manual. Are they there?

 

If the fan goes off at 40mph I just may let it be. If it does not maybe it has been this way for awhile and that would account for the fan motor burning out.