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Alternator malfunctioning- result of a bad PCM?
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MollieHughes
New User
Jul 1, 2011, 10:37 AM
Post #1 of 2
(3216 views)
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Alternator malfunctioning- result of a bad PCM?
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So first my battery died, it was actually bad so I bought a new one, then my alternator went out, which I figured was happening cause it was having a hard time when my AC was on running well, the engine would stumble a lot.
I replaced the alternator after getting it tested and finding out it had a bad diode, and just did it myself since it was really an easy fix in my car and I just borrowed some tools to do it.
Then I got it tested again and replaced a second alternator because it seemed like I had a faulty alternator again and it was running at just 11.34, but when I went back to O'Reilly's because it STILL wasn't working, they sent me over to a shop because it seemed like some bad wires.
I'm 20 years old, I don't know much about cars, I try to learn what I can but obviously there's a lot to learn. If something happens with my 2001 2.4L Oldsmobile Alero(188,000 miles) my boyfriend fixes it or gets it fixed, but he's gone this summer so I have had to do it on my own. The shop has had it for nearly a week, I'm freaking out because I'm not able to afford a big bill! I have money saved up, but that's for school, not for my car.
I've been researching it and it looks like it might be the PCM, which is what my mechanic said he'll look into next...would that cause the alternator to read out wrong? My alternator is reading at about 11.74, but apparently it's fully functioning regardless of what it's testing out as, apparently that's only how much is going into the battery. The wires and fuses have been tested and they're all good.
Also, when my car is running the alternator gets really hot. And I don't know if it's obvious or not with what my alternator is putting out, but my battery is not holding a charge.
And for some reason when I turned my car off my gauges would jump around on my dash...I don't know if this is relevant, but it's something I thought I would mention.
Please help me, because if I can know what my mechanic is doing to my car, I have less of a chance of being ripped off. I live in a tourist town, so lots of mechanics around here do that, and people think I'm naive, being a young woman, but I try not to be. I try hard to understand what's going on with things that are important to me. I need my car, I can't take a taxi every time I need to go somewhere(It adds up!) and my job has late hours, I'm often there until midnight. As a young woman I can't be out walking very much late at night, that's not safe.
I know when I need help and when I can do things by myself, and I tried researching this but I just haven't found the answers I'm looking for. Thanks so much.
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zmame
Veteran
/ Moderator
Jul 2, 2011, 9:03 PM
Post #2 of 2
(3196 views)
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Re: Alternator malfunctioning- result of a bad PCM?
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There are few different methods to use in a charging system knowing them will give you a better idea of how to diagnose them.
Old school uses transitiors, zener diodes and diodes to regulate the voltage, some manufatures still use this method.
Alot of the newer vechicals regulate voltage by PCM. the way it dose this it through duty cycles pcm will tell it to turn on and off really fast to keep a constant 14.7V (aprox). so it will increase or decrease the amount of time that it's on depending on load. It's usally controlled by the ground side of the regulator built into the alternator.
Make sure you have power at one of the connectors at the alternator (key on engine off). You should also use a 12v bulb to put a load on the power line make sure it can handle a load.
Also make sure the big, red cable has 12v going to it too. If that all passes you'll need to obtain a wiring diagram to see how it's controlled in your specific vechical.
Best of luck
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