My 2000 Regal LS started having an odd problem this week. The two cooling fans behind the radiator have been running whenever the engine is running. They do not come on if the key is in the accessory or run positions, but they do come on at the same time after the engine starts, after a delay of approx 1 sec.

I looked over the wiring diagram in the GM service manual and it looks like the PCM is commanding them to turn on. (i.e. probably not a bad relay, since if the relay were bad, they would tend to run even without the engine running.) I am not seeing an overheating warning light come on (except on start up when it comes on and them turns off like normal). Could it be a bad temperature sensor ?

Am also wondering if it could be something with the compressor. When I cycle the climate control through fan/vent/AC etc. I do not hear the clutch on the compressor click on like I usually do.

It has been abnormally cold this week, so I don't know if that has anything to do with it.

Thoughts ?

Welcome to AF.

It may be a result of the cold but it is hard to say. The fans will turn on in three conditions. With AC turned on, when the PCM module senses the engine is overheating > 220 degrees (resistance of the ECT sensor is towards low resistance or zero ohms) or when the output of the ECT sensor to the PCM module is open. Check the ECT sensor resistance and make sure it is calibrated per temperature and check the ECT wiring/electrical connector.

Thanks.

Am beginning to wonder if the ECT sensor is OK. Here's what I've found this afternoon :

(a). The fans are coming on in high speed mode - when I remove the COOL FAN 1 fuse from the under-hood fuse box, only the left fan shuts off - the right one keeps going. According to the schematic in the GM manual, this would mean the system was commanded to high speed mode. So I put the fuse back and...

(b). ...disconnected the ECT sensor and started the engine again with no change noticed - both fans started up about 1 sec after the engine started. The connector looked fine - no signs of damage/wear, etc.

(c). Shut the engine off and then reconnected the ECT sensor. I then took the cover off the engine and disconnected the inline connector that connects the ECT sensor to the wiring harness back to the PCM. Using an ohmmeter, I measured about 5k ohms between the yellow and black wires looking down into the ECT sensor for an ambient temp of +28 F. So, the sensor is not shorted out or giving a really low resistance, and indicating an overheating condition. This value of resistance is a bit low according to the chart in the manual, but still in the ballpark.

(d). Turned the key to the "run" position but did not start the engine. Used the voltmeter to look between the two pins coming from the PCM and measured 5.00 Volts - just like it should be. So at least the voltage from the PCM is getting there too.

Any further thoughts ? I don't want to wear out the fan motors. Could the A/C compressor be stuck in the "on" position somehow ? Does it even come on in cold temps ?

Here are the resistance values for the ECT. If ECT checks out your PCM module may have gone South possibly due to the weather. When A/C is on the PCM module looks at the ECT signal and the refrigerant pressure reading from the A/C system lo/hi switch. The PCM 5 volt reference signal appears good based on what you have said. Then the PCM supplies a low/ground to energize the A/C compressor relay. Also, when the ECT connector is disconnected as a test the cooling fans will both come on in hi-speed after a few second delay. So I would confirm whether the ECT signal back to the PCM module is good and not open or shorted.

If the quality is not good let me know.

http://i5.photobucket.com/albums/y186/lizzywiz/ect-1.jpg

Thanks. Those values agree pretty well with what I eventually found in the manual. The resistance I was getting was on the low side, but still in the kilohm range and not low enough to make it look like an overheating condition... unless, as you pointed out, there is something going on that keeps the voltage divider between the PCM and the sensor from working properly.

I think my problem might be the refrigerant pressure switch. The compressor is not running - I can see the clutch assembly remaining stationary when the engine is running and I can move the clutch by hand with the engine shut off - so I know that it is not stuck in the "on" position.

The ECT circuit looks OK as far as I can tell.

Question : Does the ECT sensor also serve as the source for the water temp dial on the instrument cluster ? If it does, then that supports the case for the ECT circuit being OK, since my engine temp dial is functioning normally.

Thoughts ?

:2cents: Yah I think so!

If the defroster/defogger is on, the compressor is on, with alot of cars. If the compresor AC is on the fans are on.. The AC drys the air ..

Did you try the AC and does the compressor ever turn on? May like you said be low freon but thinks its working.



Good Luck.

Question: Is this a manual dual climate control C67 or automatic climate control - ACC CJ2?

The ECT is the source for the IP temp gauge via the PCM module.

Timeout on the A/C compressor. :wave: What is your current outside temperature? The A/C is not supposed to work when the outside temperature is below 40 degrees in most settings.

Thanks for the info on the ECT providing data to the instrument cluster. That's what I thought.

Regarding the A/C, yes, it will not come on b/c it has been so cold here lately. Yesterday was the first day above freezing in over a week - it got up to a balmy 33 ! So I would not expect the A/C to come on, though the compressor should kick in if I select "front defrost" on the climate control, yes ? (My Regal has the automatic climate control system.)

Thanks for the info on the ECT providing data to the instrument cluster. That's what I thought.

Regarding the A/C, yes, it will not come on b/c it has been so cold here lately. Yesterday was the first day above freezing in over a week - it got up to a balmy 33 ! So I would not expect the A/C to come on, though the compressor should kick in if I select "front defrost" on the climate control, yes ? (My Regal has the automatic climate control system.)

I have the CJ2 ACC in my '01 GS. If you check Chapter 3 of your owner's manual it states that when you go to manual mode and select FRONT button which is defrost mode:


"The air conditioning compressor will run automatically in this setting unless the outside temperature is below 40 degrees F (4 degrees C)"

Thanks.

I tried an interesting experiment. I pulled the two cooling fan fuses and started the engine up - sure enough the fans did not start. After a couple of ignition cycles, the "Service Engine Soon" light came on - the PCM had detected the missing fuses. Good. So, I put them back, and started the engine... and now the cooling fans are off. A couple more ignition cycles and the warning light went off too. It's been fine now for a couple of days. The fans have not come back on.

Am wondering if the PCM got stuck in an unusual state, and the act of pulling those fuses and forcing it to flag the fault resulted in it resetting itself once the fuses were put back in. I had the turn signal switch replaced right before the fan issue started and they did have to disconnect the battery; maybe it glitched on power up when they reconnected the battery ?

Thanks for the feedback. Thats good news. Cold weather affects electronics. Disconnecting the battery should not affect or cause the problem.

I would check with the dealer and see if your PCM module has all the firmware updates. It may just need a update or reflash.

Just an update on the cooling fan saga. They have been fine (i.e. off) for several weeks now, but we've had another cold snap (highs only in the teens, lows in the single digits) and last night, I noticed that they started running again - both in high speed mode.

I checked for any codes using a friend's laptop-based code-reader, and it did not register any trouble codes. I used this same setup after the fuse experiment (described earlier) caused the "Check Engine Light" to come on, and the reader did show a failure on the Cooling Fan 1 and 2 control circuits, which made sense since the fuses were missing. (I cleared the codes this past weekend.)

Unfortunately, this code reader software is not terribly sophisticated, so I can't tell what state all the sensors are in, but it looks more and more like a PCM problem in the cold.

Thoughts ?

Is your defroster on when the fans are running?

No - the air flow is in "vent" mode. I can even hit the "off" button on the climate control and they still run.

but it looks more and more like a PCM problem in the cold.

Thoughts ?


I agree. I would check with a local GM dealer to see what revision you have and if necessary get a revision/re-flash or get a replacement PCM module if the problem bugs you enough and the weather stays cold. You can get a PCM on EBay for under $100. Just make sure it is from the same year model Regal LS not GS.

The problem is it is not too good on your battery.