PontiacBonnevilleClub.com

My 1993 Bonneville has been overheating when it idles for awhile. I checked the coolant level and color, all good. My fans aren't turning on, and I checked and replaced the fuses. I also hooked the fans up to the battery and they started spinning, so the motors seem to be fine. I'm guessing it is either the cooling fan switch or the relays, but I can't find the switch, and I have no diagram for the relays under the Maxifuse/Relay Center top. Any help would be greatly appreciated!

http://www.compnine.com/index.php?s=1&c ... makecode=P
Try looking here. They have diagrams for your car.

The engine's computer turns on the cooling fans when the engine is hot or the air conditioner is turned on. Do the fans come on when the air conditioner is turned on?

check 40 amp fuse in maxifuse/relay panel under hood and against firewall. you have to remove plastic cover to access the panel. it will be the fourth fuse from the left as you are facing the firewall.

if OK, check fuse 5c under dash in the IP fuse block (10 amps).

if both OK, PCM could be suspect as it is one other thing common to both fans.

i doubt the problem is in the relays as there is separate relay for low and high speed fans. these relays are dependent upon voltage from the above fuses and grounds thru the PCM. they are last two relays on the right side of the maxifuse/relay panel as you are facing the firewall (low speed right most, high speed immediately to left).

The fans should come on high (both of them) when the AC is on. Verify that first.
If the AC is off, the fans won't come on until 220°.

Just went out and checked; the cooling fans DO turn on when the AC is on.

willwren wrote:The fans should come on high (both of them) when the AC is on. Verify that first.
If the AC is off, the fans won't come on until 220°.

He is correct and it really gets to me 'cause I don't like the engine getting that hot before the cooling fans start. Try putting in a cooler thermostat (like a 185 if you haven't already) if the fans do start at 220 - BC

So the fans turn on with the AC, but my car has been reaching near or above 220, probably over 230 without the fans turning on. I can drive on the highway perfectly fine because the wind does all the work anyway, but when I'm stuck in traffic or at a light I can easily watch the temperature rise to 230. I haven't had it go over 240 simply because I would pull over or start moving again.

Boom_Diggity wrote:So the fans turn on with the AC, but my car has been reaching near or above 220, probably over 230 without the fans turning on. I can drive on the highway perfectly fine because the wind does all the work anyway, but when I'm stuck in traffic or at a light I can easily watch the temperature rise to 230. I haven't had it go over 240 simply because I would pull over or start moving again.

Did you check what willwren posted?
"The fans should come on high (both of them) when the AC is on. Verify that first.
If the AC is off, the fans won't come on until 220°."

At what temp do the fans start to run? - BC

How do you know what temp the coolant is at? Your dash gauge can not be taken as gospel.

Ok so the car just likes to run hot? I haven't parked it and gotten it to 230 so it is possible the fans turn on then.

But just in case I fear Nathaniel is overheating, I can turn on the AC and that will cool down the engine as well?

Yes, that does work.

I suggest you run it until the fans do come on and verify they are working. Do not let the temp climb up into the red zone, but atleast verify they are working properly. If you don't, you could end up in BFE and then overheat for real.

On a 93, there are TWO independent coolant temperature sensors.

The first one reports back to the PCM ONLY, and is used for the cooling fan temperature for turn-on.
The second reports ONLY to the gauge. They can be off from each other by as much as 10-20 degrees.

You can see how they work in my Techinfo article: http://www.pontiacbonnevilleclub.com/fo ... =48&t=1666

Unless you take both out of the lower intake manifold and test them in a pot of hot water, you'll never know what's going on until you hook up a scantool when the car is warmed up to see if the PCM agrees with the gauge. If the PCM were to command the fans on at 220° and they were NOT to come on, you would throw a code and a light.



I suggest a DRILLED 180° thermostat and a high-speed fan override switch if you're worried about it. In the meantime, if the temps get too high, turn the AC on.

My '93 had a similar problem, but I had a scan tool and used that to discover that the problem on mine wasn't the temperature sensor. The problem on mine was the low speed fan relay.

Relay testing tip: If you don't have a scan tool to monitor the actual coolant temp being sent to the ECM, you can test the low speed fan relay pretty easily. When you jumper the 2 pins on the ECM on your '93 (you can use a paperclip to do that) to put it in diagnostic mode, the fans turn on. You can test the low speed fan relay by swapping the low speed fan relay with the high speed fan relay and see if the fans still turn on when you turn the key while the ECM is in diagnostic mode.