2001 impala ls cooling fan continuous run

big al

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#1
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MAKE:chev
MODEL:impala
YEAR:2001
MILES:201k
ENGINE
:3.8
DESCRIBE ISSUE....cooling fan runs all the time even with key off engine off. This is my daughters car so I haven't been able to diagnose it fully yet. Fan runs unless fuse is pulled, (previously has blown fuses) but all tested well during diagnosing it, now the gauge does not read at all and fan runs all the time. Does anyone remember witch sensor controls the fans and gauge. Had this problem one time before on a impala but don't remember if it was the ECT on the top by the t Stat or the one on the bottom of the intake
 

billr

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#2
I don't think either ECT sensor will cause this problem, those sensors just provide data to the PCM and it is unlikely the PCM is programmed to leave the fan on indefinitely once the ignition is off. This is probably a problem in the wiring (including relay) between the PCM and the fan motor.

Edit: when there are two ECT sensors, often one is a 1-wire unit that is only for the dash gauge, the important one for the PCM is the 2-wire sensor.
 

nickb2

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#3
Ok, trying to wrap my head around this, have seen this before many times. There are two relays for high speed fan and low speed fan function. Start there. If the circuit is blowing fuses as you state, definitely a bad ground . Very common on these 3.8l's.

I am not at my house right now, I am at my gf's place, so I cannot provide wiring. So from memory, these fan relay circuits are power on at all time/ hot at all time. I once installed a HD switch to find the short. 2$ and amp draw was fine.

Fans were on all the time key in my hand. Ended with a bad PCM. So the bypass switch was left there cuz the client did not want to pay the high price.

I did find this however,

Screenshot (10).png
 
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nickb2

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#4
You will notice that both high speed and low speed share a common G101 ground if I read right.

Now it is important to know which fans is on, key off. Engine cooling fan or HVAC fan?? or both?? That will be a dead giveaway to PCM short out or a bad ground or bad wiring harness. Driver issues are common on these models. These gm series PCM's are notorious for driver issues inside. They are just not properly hermetically sealed from the factory. Hence the reason why too many tow trucks and too little staff to fix it. I epoxy them once I get my hands in it, rarely does one come back.

Also, interrogate the BCM. It may throw a "u" code. Sometimes that helps to see which circuit went south, and cuts on diagnosis time.
 
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#5
fan relay ? swap for a test. If its the 3relay posted above have you scanned for codes? yes even if CEL is off.
 

Gus

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#6
I would be leaning towards a stuck relay.........or like Billr said, a short in the wiring in the control circuit to the relays(s)....or bad PCM(rare)...

Nickb2....a bad ground causes a fuse to blow?
 

nickb2

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#7
@ Gus, Well, maybe that was a bad figure of speech, but yes, I have often seen a circuit grounding such as a 02 heater wire grounding out on frame instead of going through the PCM and other things like that. I have also seen high resistance in ground wires, current has no where to go.

Or if a power wire and ground/neutral wire cross, increase in amps in current flow is to intense for the rated fuse, and yes, it will blow a fuse. If the object is rated for 20 amp consumption in use, and you ground it out, what do you think happens?

Take a loose ground, common for a fuse to blow.

Most of this is not the usual reason of a blown fuse. Mostly a short will do that. So maybe my terms are mixed, but I think that is what we call a short to ground.

Basically, in what I call a short, it is exactly that, a short to ground. That is why I say always check the grounds.

I hope I made myself clearer? I have a pretty good understanding of automotive wiring and it's problems, but maybe my terminology could use a good english book to redefine my wording.
 
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nickb2

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#8
I don't like using my french as an excuse, but our terms are not the same as in english. "un court circuit a la masse" is what I call a short to ground. In my book, almost any blown module or fuse that blows is caused by a increase in and or hindrance of current flow in resistance, an open will never cause a blown fuse, the object just won't work.

So, if I am saying something wrong, plz tell me so. It always give me a better understanding of my english.

This is the best I could find that goes with my understanding..


A ground fault is an unintentional electrical path between a power source and a grounded surface. Ground faults most often occur when equipment is damaged or defective, such that live electrical parts are no longer adequately protected from unintended contact.


This here is from our own site here. See red highlighted sentience.

DIAGNOSE – FUSES REGULARLY BLOWBy Carl O’Reilly

SYMPTOM SUMMARY
An electrical fuse continues to blow once replaced.

USUAL CAUSE
A fuse is designed as an electrical protection device. It is designed to blow or open the affected electrical circuit when the current flow in the protected circuit reaches unsafe levels. Once blown, the fuse prevents electrical power from reaching the devices that are on the circuit. This prevents the wires from melting causing severe damage or fire to the electrical system. Occasionally, a fuse will blow without an apparent cause. Once replaced, the system will function normally and will not blow again. If a fuse continues to blow once replaced, it is an indication of an electrical short circuit to ground. This can be caused by a failed electrical component, bare wires touching the vehicles body (ground) or something as simple as a foil gum wrapper in the cigarette lighter socket. An incorrect fuse or to low of an amperage for the protected circuit can also be the cause.
 

nickb2

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#9
In the case of the rad fan always on, it is almost always a stuck relay or a driver issue in the module. So I think that was maybe my bad wording there in the case of this thread. @Gus, thx. You made me read more in my electrical technician english book. Always good to get reacquired with another language. :)
 

big al

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Sorry guys forgot to post the problem fix. It was the harness pigtail for the 2 wire sensor. Plastic coil protector got brittle and broke on the bottom side,wire rubbed until rubbed thru. Replaced it and back to normal now. Did not replace sensor but may not be a bad idea, looks pretty bad but during testing reads out just fine. Just a recommendation at this point.
 

Gus

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#11
Parlez vous francais, Nickb2?

I think it's a case of you say toemaytoe, and I say tomahtoe....

@ Gus, Well, maybe that was a bad figure of speech, but yes, I have often seen a circuit grounding such as a 02 heater wire grounding out on frame instead of going through the PCM and other things like that.

Yes, that is called a short to ground, not a bad ground....



I have also seen high resistance in ground wires, current has no where to go.

Correct and it goes nowhere, so it won't blow a fuse......



Or if a power wire and ground/neutral wire cross, increase in amps in current flow is to intense for the rated fuse, and yes, it will blow a fuse.

Absolutely, but once again, that is a short, not a bad ground.



If the object is rated for 20 amp consumption in use, and you ground it out, what do you think happens?

Could be a 100A fuse, if you short it to ground, it will blow....



Take a loose ground, common for a fuse to blow.

No, I disagree.....a loose ground will open a circuit.....and then it will close it...it will act like a switch, it won't blow the fuse......what will eventually happen is, with all the arcing, resistance will build up at that joint, and less current will flow, not more......


Most of this is not the usual reason of a blown fuse. Mostly a short will do that. So maybe my terms are mixed, but I think that is what we call a short to ground.

Totally agree on this....


Basically, in what I call a short, it is exactly that, a short to ground.

Agree.....


That is why I say always check the grounds.

Bad grounds, do not blow fuses.......they either open circuits, or increase resistance of a circuit, which will reduce the overall current in a circuit....



I hope I made myself clearer? I have a pretty good understanding of automotive wiring and it's problems, but maybe my terminology could use a good english book to redefine my wording.

I think you have a pretty good handle on electrical circuits.....and you have explained, pretty accurately, a lot of circuits to posters who have had problems.......I just disagreed with a bad ground causing a fuse to blow......now there are some circuits, which run parallel with other circuits, and a bad ground can cause a "backfeed" condition through another circuit.....

Keep up the good work....
 

nickb2

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#12
OK, oui je parle francais.

Je doit dire que tu a effectivement raison.

A backfeed situation is always on my mind.

I am happy that we got on the right page in regardes to this. I tried to give info in Spanish. That was a doozy.

Thank you Gus for understanding my conundrum. :confused:
 

nickb2

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#13
So hard to give good info. Even when we try to give the best free info, it comes back.

My sister and mother ask me why I give so much effort here. I say cuz it is worth it. I just lost my washer, fixed it without a doubt.

My sister said to me, I am the fixer in the family. I said, are you shitting me? She said no. Apparently, I am the fixer. I really don't want that moniker.

Last week, a guy came to me and ask for advice, live, not like here on BAT auto. I said look pal, it smells like a cooked circuit. I can smell it from here.

He said, fuck you, will not spend $ for the repair. I said OK, freezze as$hole. and don't come back.