Car alternator

flyingcheesehead

flyingcheesehead

Touchdown! Greaser!
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I've got a 2001 Volvo S60 T5, and on the way home the other night I got "electrical system service required" on screen and the battery light came on.

I figured I had a bad alternator, but got a rather unexpected result when I went to test it: It's working, on and off, in a very regular rhythm. It works for about a second, cuts out for about a second, and continues that pattern. (If anything, it works for slightly less time than it doesn't work on each cycle, but the times are fairly close and the cycle takes a couple seconds or so).

FWIW, engine RPM doesn't seem to have any effect on it.

What could be causing this?

Thanks,

Kent
 
Sounds like the voltage regulator has gone wonky. Check voltage on the field wire (which may be hard to locate if the regulator is part of the alternator).
 
Somewhat of a guess on my part, but what probably triggers the "electrical system service required" is low voltage.

Since you're indicating that the alternator seems to be working (I'm guessing you're putting a voltmeter on the battery terminals with the engine running and seeing some variation in voltage since that's the easiest point to measure voltage from), the problem is probably other than the alternator.

Check that your battery terminals are tight and clean first - that's easy and free.

If that doesn't work, have the local O'Reillys (or whatever the local parts store is) test the battery and make sure it can take a charge. If that's bad, then you know what to do.

I'll wager that it's one of the two.
 
BurtM said:
Somewhat of a guess on my part, but what probably triggers the "electrical system service required" is low voltage.
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Also my assumption.

Since you're indicating that the alternator seems to be working (I'm guessing you're putting a voltmeter on the battery terminals with the engine running and seeing some variation in voltage since that's the easiest point to measure voltage from), the problem is probably other than the alternator.
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The alternator does work, but with about a 40% duty cycle and a very regular on-off pulse. It's also very obvious with the interior lights on, as they get bright and dim, and when they brighten up the engine has a momentary slight RPM reduction as the additional load of the alternator is put on it.

If that doesn't work, have the local O'Reillys (or whatever the local parts store is) test the battery and make sure it can take a charge. If that's bad, then you know what to do.
Click to expand...

I don't know how that would cause such a regular pulsing, though.

Everyone (I've also posted on car forums) has suggested things that should result in an irregularly intermittent or complete failure. I haven't heard any ideas of issues that would result in this particular failure mode - It's got a very stable rhythm of on-off-on-off going, which shouldn't be characteristic of something being loose, a bad battery, etc. unless I'm not understanding the mechanism of failure.

I'll wager that it's one of the two.
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I'd take that bet, only because of the regular rhythm thing. Very odd.
 
Dying regulator - maybe temperature related? Microprocessors can change internal temperatures very quickly depending on current draw - if you've got a flaky controller that is on the verge of dying it could start pulling current to the field in response to a dropping voltage, overheat, and drop out until it cools down. Lather, Rinse, Repeat. I've seen it before - 1-2 second cycles are entirely possible.
 
flyingcheesehead said:
The alternator does work, but with about a 40% duty cycle and a very regular on-off pulse. It's also very obvious with the interior lights on, as they get bright and dim, and when they brighten up the engine has a momentary slight RPM reduction as the additional load of the alternator is put on it.
Click to expand...

That to me would indicate the alternator is still good.

I don't know how that would cause such a regular pulsing, though.

Everyone (I've also posted on car forums) has suggested things that should result in an irregularly intermittent or complete failure. I haven't heard any ideas of issues that would result in this particular failure mode - It's got a very stable rhythm of on-off-on-off going, which shouldn't be characteristic of something being loose, a bad battery, etc. unless I'm not understanding the mechanism of failure.
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On the basis of intuition, since the voltage increase/decrease is rhythmic, I'd say the voltage regulator is still good, too. I'd guess that you could spend a lot of time under the hood looking for a separate voltage regulator, but my 2 Pesos says the regulator is internal to the alternator, like GM started doing in the early 1970s.

I'd take that bet, only because of the regular rhythm thing. Very odd.
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I think we can assume the field wire circuit to the alternator is good, given what you've been describing. Might be worth looking at the output terminal of the alternator to make sure that's clean, though.

If all the connections are clean and the battery tests good - how hard is it to pull the alternator? That could be the problem, but modern cars can be a big PITA to do something that should be simple. If the other things we talked about don't fix it, then pulling the alternator and taking it to the parts store where they can spin it up and test it would be the next step.

Best of luck to you - electrical gremlins in cars and truck are a major PITA.
 
airguy said:
Dying regulator - maybe temperature related? Microprocessors can change internal temperatures very quickly depending on current draw - if you've got a flaky controller that is on the verge of dying it could start pulling current to the field in response to a dropping voltage, overheat, and drop out until it cools down. Lather, Rinse, Repeat. I've seen it before - 1-2 second cycles are entirely possible.
Click to expand...

That is entirely possible. Back when I was the default neighborhood wrench, most of the GM AC/Delco alternators that failed were due to the diode bridge rectifier internal to the alternator, rather than a physical failure of the alternator itself. Fixing that was pretty simple - you'd split the alternator in half and the regulator assembly was in the back half of the alternator. Change that and replace the brushes and they would be good to go for several more years.
 
If you want to source a replacement, buzz me tomorrow and I'll see what I can dig up.
 
Excess current draw? Is there any kind of thermal overload device on the output that could be performing its design function?
 
Graueradler said:
Excess current draw? Is there any kind of thermal overload device on the output that could be performing its design function?
Click to expand...

Overvoltage protection on the field wire is common. It's part of the voltage regulator. Field voltage controls alternator output (current).
 
Well, it's a moot point anyway now. I'd hoped to fix it myself, but I ended up having to use the car unexpectedly today, and on my way home the alternator quit entirely, leading to somewhat of a cascading failure, at least in the eyes of the computer - First it warned of ABS failure, then complete brake failure, telling me to pull over safely. I'm not sure if the computer shut the engine down after that or if I just lacked the juice for a spark, but that was the end of my driving for the day. Called a tow truck.

I'm sure the shop will probably just slap a new alternator in there and that'll be the end of it. Still a very odd failure mode, but I guess I'll never know for sure what caused it.
 
I Googled around for ya last night and after reading numerous stories of really strange failure modes that all eventually led to "we just replaced the alternator", I probably should have posted that. But it was all too weird to seem believable.

They'll also have the right gear to reset the codes in the computer which was another common complaint of the DIY alternator replacement crowd. They all complained that dealerships wouldn't assist and many of the odd codes are designed not to clear on their own.

You'd end up spending at least another $100 maybe $200 on the gadget to dump and clear the more esoteric (read: non-OBD II) codes that car will remember. Probably better to just let 'em fix it.
 
My last vehicle gave no indication that the alternator was failing until the car just plain shut down on an exit ramp from the highway. Same deal - cascading failure of stuff - first indication was the airbag lights, followed by some other idiot light, followed by shutdown of the fuel pump and injectors.

I was 3 blocks from home, so a quick-charge with the other car managed to get enough juice in the battery for me to get it into the driveway, where I replaced the alternator the next day.
 
Clark1961 said:
Overvoltage protection on the field wire is common. It's part of the voltage regulator. Field voltage controls alternator output (current).
Click to expand...

And there's a fuse for that, usually in the box under the hood. Probably wouldn't have any indication that the alternator was working as the OP suggested had the field circuit fuse opened, though.

But the more complex cars get, the weirder the failure modes get. I had an Oldsmobile that went wonky - dash gauges went intermittent to out completely, the power windows quit, and I don't remember what else stopped working - but the car ran fine and the fuses for the affected circuits were good. Turned out to be the body control module, which is a secondary computer about the size of a pack of cigarettes that was buried under the console. Wish I could say I figured that out myself, but that took a trip to the mechanic and $300 later all was well.

I guess that's why we still fly with magnetos just like Grandpa's Farmall.
 
My Yukon had a recall on the instrument cluster. The servos were known bad and fail sticking needles at specific numbers, or causing erratic operation.

Read that again. Had. The government let GM put a *mileage limit* on bad electronics.

It's a relatively simple fix, unsolder and replace all the servo motors (might as well replace the light bulbs with LEDs while you're in there) and solder in new ones with the proper lifespan.

My truck was under the recall mileage limit when I bought it, of 60,000 miles... But didn't exhibit signs until 75,000 miles. Then a simple Google search told me exactly what was wrong.

So I put up with it. Every once in a while I'm apparently doing 65 still after I get off the freeway and am sitting at the light.

Even funnier, the fix is to start the vehicle at which time the servos are banged off their lower stops to calibrate them, but GM only turns the speedo servo about 10 MPH worth of degrees at each engine start.

So you start, shut off, start, shut off, start, shut off... six times if it stuck at highway speed. ;)

One of these days I'll get the stupid servos ordered and spend a "quality" evening fixing a recalled component that GM got away with limiting by miles instead of being required to replace them all. Who needs a working speedometer anyway? NHTSA doesn't think you do.
 
BurtM said:
But the more complex cars get, the weirder the failure modes get. I had an Oldsmobile that went wonky - dash gauges went intermittent to out completely, the power windows quit, and I don't remember what else stopped working - but the car ran fine and the fuses for the affected circuits were good. Turned out to be the body control module, which is a secondary computer about the size of a pack of cigarettes that was buried under the console. Wish I could say I figured that out myself, but that took a trip to the mechanic and $300 later all was well.
Click to expand...

I had an issue similar to this with my 2006 Chevy, at 186,000 miles it suddenly started acting like the transmission had turned loose. It would only use second gear, would not shift at all no matter what speed, and the torque converter would not lock up. My troubleshooting convinced me that something else was wonky and the transmission itself was fine - ended up being a contact in the ignition switch that was supplying power on startup (or not, as was the case) to a separate computer module that ran the transmission. If that computer didn't have power it defaulted to the mode I saw. $40 ignition switch and life was good. I still have that truck today, at just over 251,000 miles and going strong.

I drive an old truck so I can fly an old airplane. :D
 
My old '88 325is died when the alternator quit. The battery ran out of juice to power the spark.

Anyway, I second the voltage regulator and I suspect it finally led to the death of your alternator. You might consider replacing the battery at this time, too. Then you would be covered on both ends.
 
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