Cooling Fan/Temp Gauge Problem

[White92Cutlass]

Sometimes while driving, my temperature gauge will jump into the red and back down to normal two or three times causing the "check gauges" light to come on. I'll pull over and pop the hood, but the car does not seem to be trying to overheat. Also, I cannot get the secondary cooling fan on the passenger side to come on for any reason. Below are things I have tried so far:

 

*Checked coolant level- fine

*Put car on ramps and bled air out of coolant

*Checked to make sure both the upper and lower radiator hoses were getting hot- they were

*Checked fuses and replaced the fan relays under the hood

*Replaced the temperature sender unit

*Pushed down on fan relay to see if fan would come on- it wouldn't

*Let engine run for over an hour- giving it gas at times to see if secondary fan would come on-it didn't. Primary fan always kept the temperature in the normal range during this time

*Turned A/C on multiple times while running to see if secondary fan would come on-it didn't

*Unplugged both cooling fans and tested for power with test light while engine running- both fan harnesses lit the tester up

*Unplugged the secondary fan harness and let it hang under the car- plugged two extra cooling fans I had laying around into the      harness and tried the above stuff to see if they would kick on- they didn't

*Checked for burned or broken wiring- didn't see any

*Checked to see if A/C Clutch spins when A/C is on-it does

*Checked interior heat- it's hot

 

Can someone help me out with this? Thanks!

 

[Imp558]

I'm not sure sure those two things are related, or that there's a fan problem.

Let's start with the coolant temp gauge:

 

GM vehicles from that era had a separate sender for the Gauge and the PCM, so just because the gauge spikes it doesn't mean the PCM saw the same thing.

According to Alldata your car has the 2 senders separate so the CTS for your gauge has a single green wire run to it. (Some cars have a combo sensor with both in one housing) If that wire goes to ground or it's resistance goes close to ground it will spike the gauge and if that resistance is lower than 60 something ohms it'll pop the gauge warning indicator.

 

For troubleshooting you would have someone sit in the car and watch the gauge, Key-on-engine-off and watch while you wiggle the harness under the hood and dash around to see if there's a spot where a wire is shorting to ground. If no place exists where the wiring gets an intermittent ground then the sender or gauge are bad.

 

I'll address the fans in a separate post.

[Padgett]

Assuming this is for a '92.

 

Part of the problem is that GM does not consider a car to be overheating below 250F. I had to reprogram mine to work with a 180F thermostat & fans to come on at 185 (LO) and 189 (HI).

 

Second the AC must be charged to come on with the AC selection.

 

Third, to check a fan you need to remove the relay, verify that you have 12v at the contacts, then jumper the contacts. Us at least #20 (18 is better) wire.

 

ps erratic operation is often a bad thermostat.

 

pps something is niggling the back of my brane about two ALDL contacts you can jumper to turn the fans on. Anyone know ?

Edited October 15, 2016 by Padgett

[Imp558]

*Unplugged both cooling fans and tested for power with test light while engine running- both fan harnesses lit the tester up

 

 

First of all if there's power between the Black/Red & Black wires on the fan plug then the fan should be on, you've either got a population of bad fans or there is a crummy connection somewhere so you can check for. There's a crimped splice on the way to ground somewhere in the harness and crimped connections in the back of the plug and at the relay.

 

I'm assuming the problem is going to be a poor connection that simply isn't able to move enough current to run a fan because you found power AT the fan plug but just to be thorough I'll go over the whole system.

 

The PCM has control over the fan relays via a sinking control, so the PCM will ground the control wire to trigger the relay. With that said there should be power to the other side if the relay coil with the ignition on. Your car has brown wires to the relays for this so the brown wire should have power with the key on, and the Blue/White wire on the secondary relay will get grounded by the PCM when the PCM wants the fan on.

 

Now we have to look at events that trigger the fans, the primary is pretty simple, the PCM sees a ECTS temp of 224 degrees F or so and grounds the Green/White wire on the primary relay to turn the primary fan on. When the temp gets down to the lower threshhold the PCM removes the ground from the wire and the relay and fan turn off.

 

The secondary fan is a bit trickier, the temp is up beyond the primary fan, like 230 - 240 something, I'd have to look it up. But if the temp never gets up there the secondary fan will not turn on because that criteria hasn't been met.

As you said A/C can turn on the secondary fan too. The

PCM is looking at the 3 wire A/C pressure sensor to do this and deciding if the A/C pressure is high enough to want to initiate cooling of the condenser.

In a GM vehicle with non functioning A/C it's perfectly normal to never see a secondary cooling fan come on, providing the primary fan is getting it done.

[mfewtrail]

White92Cutlass: Did you test the ground at the fan harness or just grab a ground elsewhere under the hood when testing for power at the fan plug? What type of test light are you using? A LED one or one with an incandescent bulb. If incandescent, it should be glowing brightly and not dim.

 

 

@ Padgett: Jumpering A and B slots in the ALDL on cars up to 1993 will engage both fans and flash out any stored computer codes via the SES light. A is the top right position, B is directly left of it. A paper clip or short piece of wire works perfectly for this.

Edited October 16, 2016 by mfewtrail

[White92Cutlass]

Thanks for the replies. 

 

Imp558-  I will have someone watch the gauge while i move the wiring and I'll check out the fan wiring more closely. I have already replaced the temperature sender unit. A/C blows cold.

 

Padgett- I will check the relay voltage and jump the relay. I wouldn't mind if it was a bad thermostat as they're pretty easy (and cheap) to change out.

 

mfewtrail- I grounded the test light to the car body. Should I have used the fan ground wire? The tester has an incandescent bulb and burned brightly when testing the secondary fan (equally as bright as the primary fan harness did). I'll be jumping the ALDL to check fan operation- thanks for the locations of A and B.

[mfewtrail]

Since your light glows just as bright as on the other plug w/ the working fan, I would be looking at the ground for the fan plug. Clip your test light to battery positive, and probe the ground side of the fan harness to see if your test light glows.

[Imp558]

What did this turn out to be?

[White92Cutlass]

mfewtrail- I will try that

 

imp558- Didn't have time to work on it this week-been working on other cars- and now I'm sick so it will probably be next weekend or so before I get a chance to mess with it.

[White92Cutlass]

Had a few minutes to mess with the car today-

 

Jumped the ALDL twice and both fans came on

 

Removed primary and secondary fan relays and touched the prong slots on each with a test light. One slot on each relay spot lit up- the one closest to the passenger fender

 

Pulled both fan harnesses and probed them with the test light while the light was hooked to the battery positive. The wire on each harness closest to the driver side lit up on each. Grounded the test light and probed again- no light on either harness when grounded. Started car and let it run for a little bit and the primary fan came on.

[Padgett]

If both come on with the ALDL jumper then the wiring and the fans are OK. This leave the coolant temperature sensor and the ECM. Lo fan should be on with AC or at 223F. High fan does not kick in til over 227F.(reprogramed mine to come in below 190F (appropriate for a 180F thermostat)..

[White92Cutlass]

If both come on with the ALDL jumper then the wiring and the fans are OK. This leave the coolant temperature sensor and the ECM. Lo fan should be on with AC or at 223F. High fan does not kick in til over 227F.(reprogramed mine to come in below 190F (appropriate for a 180F thermostat)..

 

 

Since I already replaced the coolant temperature sensor, the ECM is the only other possibility? ECM most likely causing both the fan issue and the bouncing temp gauge issue? 

 

If so, I have ECMs from from a 1991 Cutlass Supreme Convertible and a 1993 Cutlass Supreme Convertible. Both are also 3.1 cars, If I remember correctly, the '91 ECM will work in my '92 but the '93 won't due to transmission differences. Is this correct?

 

Also forgot to mention that I moved the wires under the hood with someone watching the gauge and no bouncing was observed.

[Nas Escobar]

For whatever its worth, I put a 92 computer in my 93 Z34 but that was an LQ1.

 

If anything use the newer computer and if it acts funny, swap the memcal