Battery & Alternator Troubleshooting

[kennethsime]

Hi all, hoping for some advice. In 80k miles and 3 years, this is my first time dealing with electrical issues. Bear with me, I've tried some searching and will search some more, but I don't know much about electrical so I figured I'd just offer a thorough explanation.

Today while on a 90-mile highway trip my battery light (generator light according to the owner's manual, which I'm pretty sure means alternator) came on. After reaching the destination I got the owner's manual out and checked for the light, which said the alternator or the belt may be malfunctioning. I checked the belt, it looked fine (no noticeable wear, felt tight, etc). I kept driving on it without issue for another hour or two before stopping to do my 20k mile service out at my parent's place.

After driving into town and stopping once more, the car failed to start. It didn't even turn over. Looked up the troubleshooting guide here on TDIClub, the starter solenoid clicked appropriately. Called autozone to get some advice, they agreed the battery was likely at fault and I should bring it in to be tested. Call a friend for a ride, start taking the battery out, and they suggest trying to jump the car and drive it to AutoZone instead. Sounds like a good idea, as soon as the Jetta is on cables it starts right up and drives fine.

At Autozone, they tested the battery, said it wouldn't hold a charge, and suggested a new one. Luckily I have my tools with me, get the new one installed, and the car starts up fine! However the battery light is still on. On top of this, on the 90-mile drive home, I felt like my headlights were fairly dim (although this could be my imagination).

So my question is: I fear (after reading a bit) the real problem is that my alternator isn't charging/maintining the battery, because the pulley slipped or a belt really is loose or the alternator is bad (please god no). Does my experience scream one thing or another to you, experienced TDI troubleshooters and/or gurus? Links and advice appreciated.

Forever in your debt,
Kenneth

 

[Ol'Rattler]

Unless you don't like your car, don't take it to AutoZone. They probably sold you a battery for a gasser which does not have the correct AH (ampere Hour) rating for a TDI. Also, a battery needs to be fully charged to be tested. Testing an almost dead battery wouln't really tell you much.

Did you check charging voltage with a voltage meter? It should be about 13.5 volts at idle. If it is 12 volts or less, the alternator is not charging.

Your alternator has a one clutch in the pulley and if it is slipping, the alternator will not charge. To check the pulley, remove the belt, block the internal fan inside of the alternator with a screwdriver and try to turn the pulley by hand. It should turn smoothly in one direction and not turn in the other direction.

Report back with what you find................

 

[akskibum]

I was just typing the same thing. To keep it short. You really can't check a dead battery and a $10 multimeter from the grocery store is more than sufficient to help diagnose your alternator.

 

[Ol'Rattler]

Even with a cheap multimeter, to check it's accuracy, you can read the voltage on a system you know is good to get an idea of how many volts indicated you should get on the suspect car.

 

[keaton85]

Check the pulley, voltage and don't listen to autozone for a thing.
A simple digital volt meter will do you wonders!

 

[curtludwig]

The super cheap multimeters from Harbor Freight are surprisingly good. I think I paid $3 for mine. I use it when I don't want to risk losing or damaging a nice one.

 

[RT1]

Charge light on is an alternator problem, not a battery problem. Your car was about due for a new battery (which I would have recommended you get from a VW dealer... one of the few items they sell that isn't a rip-off), but that wasn't the source of your problem. Check the tensioner on the aux belt path and check the pulley on the alternator. To check the pulley remove the belt and block the alternator fan from turning by inserting a a stick of wood or a screwdriver in the vent holes to block the fan blades. Be careful not to nick the windings.

With the alternator blocked from moving turn the pulley by hand. It should turn freely one way and not at all the opposite way. If it turns both ways or locks up both ways it needs to be replaced. If it checks out, move on to the alternator. Check the connections and as others have said get a multi-meter, even a cheapy one because you can't tell a thing about the charging circuit without it. If it's not charging at 13+ volts it's not charging and you need to see if the regulator is replaceable. If not, new alternator (or junkyard variety)

 

[kennethsime]

First off, thanks for all the answers given so far. I finally went out and bought a multimeter, and to my surprise, after sitting for a week, the car started no problem.

Here's what I recorded:

Car off, MM reads 11.38-11.39
Car on, MM reads 10.45
Car on, Headlamps on, MM reads 10.45
Car on, Headlamps on, Heater & Fans at full blast, MM reads 10.5
After shutting off car and waiting ten minutes, MM reads just above 12 (12.05).

From this, it seems like the alternator is not charging the battery.

Removing the serpentine belt to check the alternator pulley sounded like a breeze, but I'll have to research that a little more before I feel comfortable with it.

I did notice something I hadn't before, a regular clicking sound coming from the alternator or near it.

 

[nateinnb]

Sounds like you're right and the alt isn't charging. Removing the belt is a breeze if you've got a little strength. Depending on your set up, jack the car up on the passenger side, take off the belly pan and the inner wheel plastic if you still have them. On the tensioner there is a built in 16mm bolt. Use the box end of a 16mm wrench and get on that with the open end of the wrench basically at the 5 o'clock position. With it securely on the tensioner, push and hold the wrench towards the firewall (towards where your passenger would be sitting) with open end at about the 8 o'clock position, thus removing the tension from the belt. Remove the belt from the A/C pulley with a screw driver or by hand and slowly put the tensioner back in place. Then, remove the belt completely. You could use a pipe or something on the end of the wrench if it's not long enough for you to work with.

Looking into the engine bay, locate the alternator and you'll see the fan inside on the right close to the regulator. Stick a flat head screwdriver down in there and grab the alternator pulley with your left hand. Your pulley should turn counter clockwise but not clockwise. It may not turn either way being seized or turn both ways meaning the pulley is bad. If it seems to be functioning ok your alternator could still be faulty and you'll need to take it out and have it tested or replaced. Make sure you check all your connections etc too.

 

[Scoutx]

One more thought.

You may wish to double check the condition of the electrical connections to the alternator. Perhaps something came loose, or you have a corrosion issue.