Burning through alternators

I have a 99 volkswagon passat. I’ve replaced the alternator once a month for the last three months. Other than the belt, what could cause me to go through alternators so quickly. Also, this may or may not be related but as the alternator deteriorates my drivers side window which is automatic becomes more difficult to roll down. Then works perfectly after the alternator is replaced.

If your battery is failing, the alternator will be working harder than designed all of the time to recharge it. That can kill it easily.

The next thing after that are if the wires that connect the battery to the car are loosely connected, or are damaged. This creates higher resistance, which helps kill the alternator, too. Replace both of them as a set.


Start out with all the standard diagnostic starting/charging system tests (including a parasitic draw test). You have moved past where the freebie Auto Zone electrical system check out will be sufficient. It these tests fail to indicate the trouble you will have to pull one of these alternators apart and see exactly what failed.

One question, is the red “battery” symbol lighting up when it should and no glowing or flickering? also a look at TSB’s should be preformed, you just may get lucky and find a report from VW about this.

As per the usual, there’s a few unanswered questions.
Are you sure the alternators are really bad?
Who is doing the diagnosis and how is it being done?

If the wiring between the alternator output and the battery hasn’t been checked for a problem then that needs to be done. There may be a bad connection there. The battery sense lead to the alternator also needs to be checked out to see if a problem with it is causing the alternator to go to full output all the time.

No, the battery symbol came on and stayed on. There was no glowing or flickering. Reving the engine did not help. The alternator quit working completely and was just running off the battery.

No, I guess I’m not sure the alternators are really bad. I’m trusting a local mechanic and I don’t really know how the testing is being done.

It seems that you have a short in the driver’s side window circuit. Maybe not a complete short but there is some amount of draw to ground.
Alternators don’t do well with any kind of short to ground. More so than in the past, your alternator will slowly fail as the diodes fail. Your battery is being drained and your alternator (new or replaced) is working overtime to charge the battery while the diodes are being damaged by the draw in the window circuit. Disable this circuit via the fuse and see what happens. If I’m right your new alternator should survive just fine until you replace the fuse.

Does the battery light operate normally with key on engine off?

Just my opinion, but if a mechanic is charging you for this then it’s his responsibility to figure out why the alternators are going bad IF that is the case.

There’s other reasons for an alternator to refuse to charge; erratic connection in the dashboard warning light, weak link between the alt. and battery, etc. and even the belt can be an on and off thing.

Yes it does.

Also are those rebuilt alternators? Some rebuild shops are not very good and could easily have provided rebuilds with problems.

It sounds incredibly frustrating to be going through alternators so frequently on your Passat. As someone who relies on my car, I understand how difficult repeated repairs can be. I wonder if there could be an electrical drain or short somewhere that is placing extra load on the alternators, wearing them out prematurely.

The connection with the driver’s window is also concerning. Perhaps there is damaged wiring running to both the window and alternator that gets worse as the alternator fails. I would recommend having the Passat thoroughly inspected electrical system inspected for any shorts, damaged wires or excessive loads that could be causing the issues. Replacing wiring harnesses may be pricey, but could save money in the long run by fixing the underlying problem.

For more details, you can visit guide: