Bad Alternator = transmission problems? Really?

[ZepSL2]

ok so A few weeks back I start to get the dash battery light coming on about 10 seconds after i start up then it would go out after driving for about 2 minutes. Been Doing that since then and why I delayed getting it fixed. If the light came on and stayed on i would have been more motivated to fix it that very day

Anyway 2 days ago I started getting P0732 P0733 P0734 codes. I have an ultragauge (awesome tech BTW has 72 gauges etc.. and just $59) So i can see the codes and clear them also. So i hop on here and start searching.

My jaw hits the floor when i see some people mention that a bad alternator may affect transmission. So i get off my arse today and buy a digital volt meter and i just checked the alternator under load and not under load.

Alt under load = 13.82 (headlights , heater , rear defroster - all on)
Alt NOT under load = 14.21
NOTE : battery light NOT ON during this test i will have to re test next time
when the light is on and compare)

So does this appear to be a bad/failing alternator?

If so how the heck can it cause such major transmission errors/problems?


I cleared the codes last night when i got home and today i drove 120 miles and no codes. (Battery light did come on before i left . I did the check when i got home just a few minutes ago)


thoughts?


thanks!

[fetchitfido]

Autotragic's are very sensitive to how the electrical system is working. Sounds like you may have a slipping belt, not turning the alternator properly all the time. Check the tensioner too, that may be worn out & in need of replacing.

[OldNuc]

The battery light will come on when the alternator voltage is below the battery voltage. This is the way it works and there is no computer or other magic involved.

Your static voltage check does establish this as an intermittent problem. Go to a good parts store and ask for the battery/alternator to be tested. You can have adequate voltage and inadequate current.

Serpentine belts are not known for slipping but if the tensioner has failed it will slip under load when cold. The original OEM tensioner will fail and not clank so check the belt and tensioner.

[PlasticCarsRock]

Originally Posted by OldNuc

The battery light will come on when the alternator voltage is below the battery voltage. This is the way it works and there is no computer or other magic involved.

Sorta. Unlike older cars, the battery light is controlled directly by the digital regulator. It grounds its end of the connection (the other side of the bulb always has power) if the voltage at the alternator is too high or too low (based on preset parameters). Too high is very unlikely, but possible, with a failed regulator.

Originally Posted by OldNuc

Your static voltage check does establish this as an intermittent problem. Go to a good parts store and ask for the battery/alternator to be tested. You can have adequate voltage and inadequate current.

Not anything that a test at the parts store would be likely to find. They measure the same thing he did: battery voltage unloaded, and loaded with your car's own accessories. If it drops below a certain threshold, it will indicate a failed alternator (I don't know the exact number, but it's something like 13V unloaded and 12.5V loaded).

The only way to have adequate voltage and inadequate current is if there is some form of resistance between whatever you're referencing, presumably the alternator and battery. If this were the case, the battery voltage would be lower. Given a low resistance, you cannot have voltage without enough current (note that the current can be quite low, if the battery is fully charged and no accessories are on).

Originally Posted by OldNuc

Serpentine belts are not known for slipping but if the tensioner has failed it will slip under load when cold. The original OEM tensioner will fail and not clank so check the belt and tensioner.

This is my best guess. When you first start the car (after it has been sitting for more than an hour or so), the alternator is heavily loaded, trying to charge the battery very quickly. With a bad tensioner, bad belt, or contaminated (slippery) belt this will cause the belt to slip and the alternator not to charge sufficiently (or at all). It's typically (but not always) accompanied by a loud squealing noise.

First, clean all the pulleys and belt with something like brake cleaner. Make sure there is reasonable tension on the belt. If that doesn't help, try a new belt (make sure it's a 778 belt, not a 780 belt, as both are supposedly for the car, but a 780 will typically be too loose (particularly with aftermarket tensioners). If you still have the problem, look into the tensioner a bit more--check deflection of the belt between pulleys, and if necessary , replace the tensioner.

(Or do it my way: replace the belt twice, then the tensioner (with something far worse that what the car had), then find out that the belt is just contaminated and fix the problem by cleaning it with brake cleaner.)

[OldNuc]

The parts store will do a proper load test and It will show a defective alternator drive.

Sorta. Unlike older cars, the battery light is controlled directly by the digital regulator. It grounds its end of the connection (the other side of the bulb always has power) if the voltage at the alternator is too high or too low (based on preset parameters). Too high is very unlikely, but possible, with a failed regulator.

Not, "sorta" it is exactly what turns on the light, a voltage differential between the alternator output and the battery terminal voltage.

The only way to have adequate voltage and inadequate current is if there is some form of resistance between whatever you're referencing, presumably the alternator and battery. If this were the case, the battery voltage would be lower. Given a low resistance, you cannot have voltage without enough current (note that the current can be quite low, if the battery is fully charged and no accessories are on).

Above is incorrect. Back to basic generator theory for you. A lack of adequate excitation or input mechanical power will result in a lack of adequate POWER out. The voltage will measure as within specs if the excitation is correct.

Cleaning a belt, any belt, with a petroleum distillate is very hard on it and shortens its life. brake cleaner is now a witches brew of alcohol and petroleum distillate. Adequate belt tension is verified by measuring the torque required to deflect the tensioner, and proves nothing if the belt has been slipping cold. Once the belt slips to the point it is noticed it is shot. Bottom line is a 100amp load test will identify a slipping belt/defective tensioner.

[kg6mvb]

Originally Posted by ZepSL2

My jaw hits the floor when i see some people mention that a bad alternator may affect transmission

This is one of the joys of modern computer controlled cars. One common reason for the transmission issues with a bad alternator is when the diodes in the alternator fail.

Your alternator (by design) creates AC voltage at a frequency that varies based on engine speed. Internally the diodes convert this to DC power, then the regulator clamps this off to make (sort of) clean DC power. If one or more of the diodes fail, you get more AC ripple than the regulator can clean up and you have this whine getting out into the electrical system of the car.

Back to the "sort of"...they all let some whine out. With failed diodes it becomes excessive.

Now in your transmission you have a speed sensor that creates an AC signal that varies in frequency based on speed.

If your incoming power from your bad alternator is bad enough, the transmission computer can get confused and interpret the alternator whine as the transmission signal. In the computer's mind, something is WAY off so it tries to fix it, sets codes etc.

[ZepSL2]

very interesting. thanks all for the replies thus far. I went out and pushed the belt and inspected it and it seemed tight and looked clean though the belt does have 74K on it (total miles is 153K) I never knew what size the belt was because I just went to pep boys and said give me a belt that works.

With all the talk of the tensioner though some things started to pop into my mind that i thought was not related until after reading everyone's replies. I happen to get this intermittent loud clanking sound at 1500 to 1800 rpm. I never was able to locate it exactly. I thought it was loose heat shield. Starting up in the morning never has the clanking but once car has been driving for about 10+ minutes roll the dice for clanking sound. I am thinking now after reading your replies that the tensioner may be bad and maybe hitting a stop or something and also bad enough now to cause belt slippage? or maybe the belt was just a bit too big when i bought it and now it is MEGA stretched/worn enough to also let the belt slip.

I guess it is time to get a new belt and tensioner. what is easiest way to tell if a tensioner is bad? Alternator i guess comes next if problem is still there after i deal with these first 2 things lol

did i miss anything?

Can anyone recommend a belt (778 I will get) and tensioner? I own a 2000 SL2 1.9L DOHC (vin 7)

huge thanks!

[R8DERHED5150]

Love the Good Year gator back. Have them on both saturns for a couple years now, visually look great. Cheap anywhere you can find'em.

I need to change my pully too, watchin for the recommendation myself here.

[OldNuc]

A 778 size belt and all of the aftermarket tensioners are poor. Pick the one you like. If you have been reading about the belt tensioner issues then you should know that here is no "good" one and having one work properly is a crap shoot. The Gates gator back belt and Gates tensioner seems to work for most.

Originally Posted by ZepSL2

very interesting. thanks all for the replies thus far. I went out and pushed the belt and inspected it and it seemed tight and looked clean though the belt does have 74K on it (total miles is 153K) I never knew what size the belt was because I just went to pep boys and said give me a belt that works.

With all the talk of the tensioner though some things started to pop into my mind that i thought was not related until after reading everyone's replies. I happen to get this intermittent loud clanking sound at 1500 to 1800 rpm. I never was able to locate it exactly. I thought it was loose heat shield. Starting up in the morning never has the clanking but once car has been driving for about 10+ minutes roll the dice for clanking sound. I am thinking now after reading your replies that the tensioner may be bad and maybe hitting a stop or something and also bad enough now to cause belt slippage? or maybe the belt was just a bit too big when i bought it and now it is MEGA stretched/worn enough to also let the belt slip.

I guess it is time to get a new belt and tensioner. what is easiest way to tell if a tensioner is bad? Alternator i guess comes next if problem is still there after i deal with these first 2 things lol

did i miss anything?

Can anyone recommend a belt (778 I will get) and tensioner? I own a 2000 SL2 1.9L DOHC (vin 7)

huge thanks!

[ZepSL2]

ok i will get the gator belt and tensioner. thanks all!