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Old 04-04-2009, 10:42 PM
silk1976 silk1976 is offline
Join Date: Aug 2003
Posts: 523
Mechanics: signs of an alternator going bad?

My car (2000 Saturn SL2 w/180k miles on it) has what I suspect is an alternator that is on its last legs. I'm not sure of the typical symptoms, so I wanted to ask others who might have a better idea.

The past couple months, I've noticed that when I start the car, the dash lights and electrical components (blower, power window, etc) work, but they are a bit sluggish or dim. This is with the car in idle. Once I start driving and the RPM's reach around 2k, things liven up - the dash lights are brighter, the fan pitch gets higher, etc. Then, when I get to a stop light, things slow down again. When I speed up, things perk up again.

I just changed the battery a couple months ago. The previous one was dead - I think it had a bad cell because the car started going all Christine on me en route - radio flickering on and off, engine just about stalling at stop lights, severely degraded power when applying the gas (I'm thinking due to bad sparks, in turn due to failing electrical circuit with the bad battery cell), etc. The old battery was a little over 4 years old, and I abused the hell out of it by accidentally leaving the lights on and draining the battery on four separate occasions within 3 months. I finally realized it was partially because the ding-a-ling idiot bell wasn't going off when I'd have the lights on and the car off. The other reason is that I've apparently become an idiot who is dependant on that bell . Anyway, long story short - the battery condition itself is fine.

I had the alternator checked out @ autozone after the battery was changed, and the diode pattern and voltage output checked ok. However, the voltage test was at 2000 RPM - not at idle.

So - my suspicion is that the 9 yr old alternator is on its last legs. But I wanted to see if there are other high degree possibilities I may not be thinking of.


P.S. - FWIW, just as a point of more information - prior to the battery being replaced, I had a succession of times over the fall of '08 when the SES light would come on with a P0442 (small evap leak) code. I replaced the gas cap about 2 years ago (spring 07) when I was getting a P0442 light and noticed the gasket on the gas cap was severely cracked. Once the battery was replaced, the P0442 codes stopped popping up - until the fall of 08 when the battery abuse began. Seems like maybe the old battery was screwing with the electrical system in such a way to trigger the sensors. I only mention this in case it might have some relevance.

Last edited by silk1976; 04-04-2009 at 10:44 PM.
Old 04-04-2009, 10:50 PM
zwede zwede is offline
Join Date: Mar 2001
Location: Plano, TX USA
Posts: 666
It does sound like the alternator is pretty much done. You could ask the people at autozone to hook up a voltmeter across the alternator with the engine idling, and then turn on lights, wipers, rear window defrost etc (put a load on it) and see how it is doing. If the voltage drops quite a bit when doing this the alternator is done.
Old 04-04-2009, 11:00 PM
Gary T Gary T is offline
Join Date: Mar 2002
Location: KCMO
Posts: 11,169
Pretty sure bet it's just what you surmised. A good alternator should be able to maintain sufficient charging voltage (~14.0-14.5 volts) at idle under load. The normal test load for this is headlights on, blower on high but A/C compressor off. You can check it with a voltmeter to be sure, but from what you describe I'd be shocked if the voltage at idle is as high as it should be.

Be aware, though, that this assumes good electrical connections. Poor connection between a battery cable and battery terminal, or at either end of the alternator's output wire (the really thick one on the alternator), could cause a problem. This should be checked and addressed first.
Old 04-05-2009, 06:44 PM
silk1976 silk1976 is offline
Join Date: Aug 2003
Posts: 523
So I put a multimeter across the battery when the car wasn't running. 12V on the spot (no surprise there).

I started the car with no blower or lights on, and it was something like 12.2V at idle. I then turned on the lights and the blower and it read 11.7V

Later in the day, my wife and I went to target. Just before we got there (after going to the drive thru at wendy's, which meant a couple minutes at idle), the car started going crazy - flashing the air bag light and stuttering. While at the stop light I put it into neutral and kept the RPM around 2000.
When we went to go leave Target, we needed a jump start.

So on to the parts store I went. Picked up an alternator, spent a few hours putting it in (after spending a good deal of time figuring out how to get at the damn thing!) and checked the voltage on the battery. Around 14.4V, and IIRC, that was with the lights on and the blower going.

Gave it a test drive - the lights stayed nice and bright and the blower spun with hurrican force winds. Looks like that did it!

Thanks for the responses - I just wanted to make sure I was reasonably barking up the right tree!

@Gary T - I took your advice and verified the connection from the alternator (once I had it up on jack stands and once I started the process of taking things apart) - it actually had a protective boot on it, so the underlying bolt was pretty clean. Not sure if all cars have that boot - but verifying that sounds like a good point.

Last edited by silk1976; 04-05-2009 at 06:47 PM.
Old 04-05-2009, 07:21 PM
Dog80 Dog80 is offline
Join Date: Dec 2003
Location: Athens, Greece
Posts: 3,354

How did the car start with the battery at 12 volts? I've seen batteries at 12.4 and the car wouldn't start. At 12 it is practically dead.
Old 04-05-2009, 09:26 PM
silk1976 silk1976 is offline
Join Date: Aug 2003
Posts: 523
Not sure - but considering its a 12V battery, I'd be concerned if it was registering significantly more than 12V.

Maybe the battery you saw at 12.4V didn't have enough amps behind it to get the starter turning? That'd be my guess.
Old 04-05-2009, 09:55 PM
Booker57 Booker57 is offline
Join Date: Mar 2000
Location: Finger Lakes area of NY
Posts: 1,602
12v is a misnomer. 12.6 volts is normal full charge. There are six cells that produce 2.1 volts each.
Old 04-05-2009, 10:01 PM
silk1976 silk1976 is offline
Join Date: Aug 2003
Posts: 523
I was just reading up on that (probably as Booker was writing his post) and I just saw that it is actually 12.6. According to the wiki entry I saw, when a battery registers close to 12V, it only has about 25% charge. Probably explains why I needed a jump start - because I had started the car, tested the voltage, shut it off, and then started the car again (a bit later) to head out to the store. So there wasn't enough time (in driving to the store) to charge the battery back up enough.

Just for the heck of it, I'll probably be checking voltage over the next few days - just cuz I'm the curious type
Old 04-05-2009, 10:17 PM
zwede zwede is offline
Join Date: Mar 2001
Location: Plano, TX USA
Posts: 666
BTW, congrats on making the original alternator last 180 K miles. The alternator in my BMW lasted all of 35K miles.
Old 04-05-2009, 10:42 PM
silk1976 silk1976 is offline
Join Date: Aug 2003
Posts: 523
@Dog80 - I somewhat owe you an apology! When you first asked how the car started, my response was basically 'well, its a 12V battery putting out 12V - just what its supposed to do!' Internally, I kinda said 'what the hell kinda question is that?!'.

However, after driving the car around earlier this evening with the new alternator in, and just checking the voltage, I see it showing 12.7.

I learned me something today

And now I'm wondering - How the hell did it start with 12V?

@zwede - I've been pretty lucky with this car. 160K miles on the front wheel bearings, no transmission problems (yet), no real engine issues (just a little bit of an oil burner). It's too bad GM is killing the Saturn brand - because I'd have no problems buying another one otherwise.
My wife and I just bought a new car to replace her 2004 Hyundai PoS w/transmission issues. I've been trying to get her to drive my car full time once we pick up the new one - I mean, mine has 180k miles of proven reliability behind it. The new car cannot say the same! After her issues with the Hyundai - she should want something proven, right? She hasn't bought into my logic yet.

Last edited by silk1976; 04-05-2009 at 10:43 PM.


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