97 Cavalier - Alternator hum with engine off - Third Generation Forum

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97 Cavalier - Alternator hum with engine off
Friday, December 14, 2012 3:13 PM
1997 cavalier. The alternator is making a high pitch electrical sound (you have to put you ear up to it to hear it) after the engine is turned off. Along with the hum it has 4.96 volts at the alt. plug. After pulling the PCM fuse it stopped. The 4.96 volts at the alt plug stopped also. I put the fuse back in and 0.0 volts and no sound. Restart the engine, the alt charges. Shut it off, and the sound is there, unplug the alt plug and have 4.96 volts. I'm thinking a relay is stuck but I'm not sure where to find it to check it . Any Ideas ? Thanks all.

Re: 97 Cavalier - Alternator hum with engine off
Saturday, December 15, 2012 11:31 AM
There is no alternator relay. Your PCM is probably bad.





i find it amusing that SHOoff has nothing better to do but follow me around & be an unhelpful dick in even cross-forum. - Jon Mick
Re: 97 Cavalier - Alternator hum with engine off
Saturday, December 15, 2012 1:48 PM
Could also be a short somewhere in the alternator.


"In Oldskool we trust"
Re: 97 Cavalier - Alternator hum with engine off
Saturday, December 15, 2012 2:35 PM
Y3llowCav wrote:

Could also be a short somewhere in the alternator.


this is what happened to mine when i had the same issue.



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Re: 97 Cavalier - Alternator hum with engine off
Saturday, December 15, 2012 11:10 PM
So best to start with alternator and go from there? Another thing I noticed is when I replaced cig lighter fuse a relay engaged and I didn't hear it click off. Is the horn the only other thing on that circuit? It doesn't work ( the horn ) .
What are signs of failing PCM ? It seems to be working . I had a code pop for o2 sensor ( wire loose ) and I was able to scan and clear codes...IDK. One other thing has me puzzled , the idle has dropped and the windshield wipers only work on high ( took switch out and tested/cleaned contacts and it is ok ) .All these things happened at the same time though they may not be related , could be multiple problems. Again any help appreciated .
Re: 97 Cavalier - Alternator hum with engine off
Sunday, December 16, 2012 3:44 AM
Check your grounds. Check the big ground on the battery tray and make sure the strap to the block is good. I still suspect the alternator. When they start going bad weird things like this can happen. Also maybe try battery terminals first. Sometimes the gm terminals get super crusty and don't make good contact. That can lead to strange problems too.


"In Oldskool we trust"
Re: 97 Cavalier - Alternator hum with engine off
Sunday, December 16, 2012 8:13 AM
Y3llowCav wrote:

Check your grounds. Check the big ground on the battery tray and make sure the strap to the block is good. I still suspect the alternator. When they start going bad weird things like this can happen. Also maybe try battery terminals first. Sometimes the gm terminals get super crusty and don't make good contact. That can lead to strange problems too.

Indeed , high/low voltage can cause weird things. I cleaned all the grounds I could find and replaced battery terminals .Its putting out 14.1 vdc but I haven't taken it off and checked diodes brushes ect.
Re: 97 Cavalier - Alternator hum with engine off
Tuesday, December 18, 2012 4:35 AM
When they engine is running the PCM sends a turn-on signal to the alternator. If your engine is not running, and the alternator is still turned on, then it is being turned on by the PCM. Which makes sense because it stopped when you pulled the PCM fuse. This should not be happening (obviously). If fact if you stall the engine and the key is still on the alternator is still supposed to be shut off.





i find it amusing that SHOoff has nothing better to do but follow me around & be an unhelpful dick in even cross-forum. - Jon Mick
Re: 97 Cavalier - Alternator hum with engine off
Thursday, January 17, 2013 6:32 AM
interesting. my 98 has a hum in the alternator that just started as well as a random no start. sounds like when i try to crank it is dead bu i can throw it in my truck and start that. i would be interested to know if the o.p. had his alternator checked out and if it was the issue.



Re: 97 Cavalier - Alternator hum with engine off
Thursday, January 17, 2013 9:43 AM
I believe my issue is a failing ecu . Can you hear the starter relay click when you attempt to start it? It ( starter relay ) is located on drivers side radiator support.
Re: 97 Cavalier - Alternator hum with engine off
Thursday, January 17, 2013 11:35 AM
yeah i can hear click and then a bunch of rapid clicks





Re: 97 Cavalier - Alternator hum with engine off
Thursday, January 17, 2013 10:26 PM
Check/clean the grounds ( especially the one on the battery tray ) and battery terminals just to rule out ground problem(s).
Re: 97 Cavalier - Alternator hum with engine off
Friday, January 18, 2013 10:01 AM
i will go over them again but when i had the car apart i cleaned and sprayed the battery (not the ground contact patch obviously.) i will go over them all and maybe run better wiring to the starter ground etc




Re: 97 Cavalier - Alternator hum with engine off
Friday, January 18, 2013 5:40 PM
After more thought that relay may still be the issue. Though not as common rapid clicking can be a sign of relay failure.I had to replace it on my daughters car but it simply did nothing so I took it off and tested it and found it to be bad. That may be the next step ( testing relay ) if all connections are good. Here is a link to a decent video showing the testing process. Your text to link here...
Re: 97 Cavalier - Alternator hum with engine off
Monday, February 11, 2013 5:14 PM
New problem; no start. Cranks fine , has fire fuel and good compression. It is over fueling and flooding the plugs. No codes and I can still read the ecu with scanner but I suspect ecu failure. Seems I would have some cel if it is a crank/cam position sensor , wouldn't I ? Any help appreciated.
Re: 97 Cavalier - Alternator hum with engine off
Wednesday, March 13, 2013 7:08 AM
1) Alternator- This is how I am thinking when I read this thread. No one notes that alternators are a belt driven system. That belt generates the batteries recharge. No movement from the belt, no power being made, not natively at least. I was thinking that the battery would be pushing the power before a chip can send it back on a open circuit. Nothing turns a alternator "on". They are a mechanical driven system working off gyrostatic and the PCM shouldn't be able to hold a charge causing the "hum". Unless the PCM bridges the power back over to the alt, but if that were the case it would resume after the fuse was replaced, because if the key is off and not stopping the unit, why would unplugging and replugging the fuse? Again I just write down what I think as I read, no particulars.





Z doesn't mean last, it just lapped A.
Re: 97 Cavalier - Alternator hum with engine off
Tuesday, March 26, 2013 9:22 PM
So did anybody ever figure this out? i just replaced my starter yesterday and noticed that i now have the same issue
Re: 97 Cavalier - Alternator hum with engine off
Wednesday, March 27, 2013 12:20 PM
ZWolf24 wrote:

1) Alternator- This is how I am thinking when I read this thread. No one notes that alternators are a belt driven system. That belt generates the batteries recharge. No movement from the belt, no power being made, not natively at least. I was thinking that the battery would be pushing the power before a chip can send it back on a open circuit. Nothing turns a alternator "on". They are a mechanical driven system working off gyrostatic and the PCM shouldn't be able to hold a charge causing the "hum". Unless the PCM bridges the power back over to the alt, but if that were the case it would resume after the fuse was replaced, because if the key is off and not stopping the unit, why would unplugging and replugging the fuse? Again I just write down what I think as I read, no particulars.


You sir, are incorrect. Pull the plug out of the back of your alternator, but leave the big red cable attached to it. After pulling that plug, drive the car around for a couple days and then come back on here and tell us that "nothing turns the alternator on"

It is not a generator, it is an alternator. One main difference is, that your alternator does not have permanent magnets inside of it, therefore you need to have something to create a field in order for it to do anything. Guess what you use to create that field? And don't get me wrong, i know that there are Self-Exciting alternators out there, but our cars just don't have them. SepEx systems are cheaper.





i find it amusing that SHOoff has nothing better to do but follow me around & be an unhelpful dick in even cross-forum. - Jon Mick
Re: 97 Cavalier - Alternator hum with engine off
Wednesday, March 27, 2013 7:15 PM
I haven't found a solution yet , but I haven't had time to look into it further. As of now it still charges well and no battery drain. The hum stops after the car is off and has sat for about 30 - 45 min.
Re: 97 Cavalier - Alternator hum with engine off
Saturday, March 30, 2013 4:34 PM
yes low or high voltage does extremly wierd things, when my terminals got correded in my 00 z24, and it would LITERERALY turn EVERY dash warning light on possible and not even crank... freaked me out, i thought something was horribly wrong, replaced my terminal botls and she was all good


John Lenko wrote:

It is bad. Stop. Now. Bad. Bad bad. Bad bad bad.

...j

Re: 97 Cavalier - Alternator hum with engine off
Monday, April 08, 2013 4:25 PM
SHOoff wrote:

ZWolf24 wrote:

1) Alternator- This is how I am thinking when I read this thread. No one notes that alternators are a belt driven system. That belt generates the batteries recharge. No movement from the belt, no power being made, not natively at least. I was thinking that the battery would be pushing the power before a chip can send it back on a open circuit. Nothing turns a alternator "on". They are a mechanical driven system working off gyrostatic and the PCM shouldn't be able to hold a charge causing the "hum". Unless the PCM bridges the power back over to the alt, but if that were the case it would resume after the fuse was replaced, because if the key is off and not stopping the unit, why would unplugging and replugging the fuse? Again I just write down what I think as I read, no particulars.


You sir, are incorrect. Pull the plug out of the back of your alternator, but leave the big red cable attached to it. After pulling that plug, drive the car around for a couple days and then come back on here and tell us that "nothing turns the alternator on"

It is not a generator, it is an alternator. One main difference is, that your alternator does not have permanent magnets inside of it, therefore you need to have something to create a field in order for it to do anything. Guess what you use to create that field? And don't get me wrong, i know that there are Self-Exciting alternators out there, but our cars just don't have them. SepEx systems are cheaper.


Correct.

I swapped my old 83 Jimmy's alternator for the CS130 style, which is what is in most all GM vehicles from the late-80's to early 90's and onwards til' the mid-2000's sometimes.

The L-Circuit needed to see a 3W resistance in the circuit, usually provided by the idiot light in the cluster. I only had a Voltmeter, so I wired in a socket and bulb, just to make it look like it was meant to be.

Just some info to bolster your argument.

-----------------------------------------------------------------
1995 Corsica and a bunch of trucks too...

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