ALH intermittent battery light flashing. Several tests done, yet still undiagnosed.

spreadpanic

Member
Joined
Oct 6, 2015
Location
Baltimore, MD
TDI
2002 Jetta
Hello all,


Two weeks ago, my battery light started intermittently flashing. The flashes have started getting more frequent, and longer.


Multimeter to the battery says 12.5v with the engine off. When engine is idling, ~14.5v. When the engine was reved to around 2000 rpms, fluctuated between high 13s and low 14s, even while the battery light flashed several times.


There is a little bit of squealing around the serpentine area. Tensioner looks a little jumpy, but not as bad as I've seen in some videos.


After removing the serpentine belt, I found all of the pulleys to spin freely, or without much resistance, in both directions. There is a little bit of bearing noise in the tensioner pulley, but still a smooth spin.


As for the alternator pulley, it spins only counterclockwise when I put a screwdriver into the housing. I am met with a little bit of resistance, enough so it stops spinning as soon as I remove my hand.


Inside the car, I checked the fuses with the battery symbol, none were blown. Electrical is not my strength.


Is there anywhere else I should start looking into? Could it just be a computer/sensor issue?
 

WildChild80

Veteran Member
Joined
May 30, 2016
Location
Nashville, AR
TDI
2001 Jetta TDI 2000 Jetta TDI 2000 New Beetle TDI ALL 5 speeds
Almost guarantee it's the clutch on the alternator
Similar issue and swapped the pulley and all is well
Sent from my Pixel XL using Tapatalk
 

steve6

Veteran Member
Joined
May 25, 2010
Location
Beaverton, ON
TDI
2003 jetta tdi
In for alternator clutched pulley as well

Funny story, I had a 2003 jetta, and I had the alt light start flashing, I was on the highway so I just kept driving, about 90 minutes later it turned off. I didn't do anything about it, about 6 months later it flashed again for a few minutes randomly, stopped and life went on. It did that every so often but never totally failed. I drove that car for over 6 years and up to almost 600,000 kms, never did change the alternator.
 

Genesis

Top Post Dawg
Joined
Feb 26, 2003
Location
Sevier County TN
TDI
'03 Jetta Wagon
Yeah, the bad news is that one day you may have a load of fun when the pulley grenades and takes out things under there. In the worst case some piece of the carnage gets behind the timing belt cover and then you're hosed.

The other alternative is that it will fail locked up hard, in which case the shock on the tensioner will be destroyed quite quickly. That's cheaper than the other disaster by a lot, but still kind of a pain in the neck.
 

mauricioezequiel

Well-known member
Joined
Aug 28, 2019
Location
Argentina- Buenos Aires
TDI
Golf mk4 Comfortline 2004 agr
Yeah, the bad news is that one day you may have a load of fun when the pulley grenades and takes out things under there. In the worst case some piece of the carnage gets behind the timing belt cover and then you're hosed.

Mine fell apart when I changed it, the only symptom was some flashes of the battery light on the dashboard when driving on the highway; and also looked quite healthy when was still attached to the alt.
 

WildChild80

Veteran Member
Joined
May 30, 2016
Location
Nashville, AR
TDI
2001 Jetta TDI 2000 Jetta TDI 2000 New Beetle TDI ALL 5 speeds
mine made a chirping sound and and the lights would dim a little

Sent from my Pixel XL using Tapatalk
 

spreadpanic

Member
Joined
Oct 6, 2015
Location
Baltimore, MD
TDI
2002 Jetta
How many miles has the alternator pulley?

I put in a Bosch reman 4 years ago, but have been living out of the country half the time, so probably only around 20,000 miles.


Based on everyone's feedback, yes, I think the pulley is the next logical step. I'm just confused why I am still getting a solid 14V to the battery at 2000 rpm, even though the battery light is flashing. I'm not good with electrical, but the constant 14ish feels like that would indicate the alt is doing its job smoothly?


It's actually still under warranty, but honestly I'd rather spend $50 on a spline tool and pulley, be done with it (hopefully) in 20 minutes, than going through the process of yanking the whole unit. I've already had to do several other things to the car this month, kinda out of time for it!
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
Digital multimeters have a lag in their response and are also not good at catching brief changes, whereas the alternator warning system flags them at the speed of light. :)
 

Rrusse11

Veteran Member
Joined
Jan 23, 2014
Location
PA Deutsch Country
TDI
2002 Golf, 5spd; 05 Jeep CRD
I put in a Bosch reman 4 years ago, but have been living out of the country half the time, so probably only around 20,000 miles.


Based on everyone's feedback, yes, I think the pulley is the next logical step. I'm just confused why I am still getting a solid 14V to the battery at 2000 rpm, even though the battery light is flashing. I'm not good with electrical, but the constant 14ish feels like that would indicate the alt is doing its job smoothly?


It's actually still under warranty, but honestly I'd rather spend $50 on a spline tool and pulley, be done with it (hopefully) in 20 minutes, than going through the process of yanking the whole unit. I've already had to do several other things to the car this month, kinda out of time for it!

My serpentine belt was showing signs of wear, spotted by my sharp eyed
guru. No symptons, yet, but investigation of the issue and my pulley was
seized. Even my pros wouldn't attempt to do it in place.
So about 3 hours total to get the alternator out and on the bench and re-installed.

Good luck with your 20 minute fix.
 

WildChild80

Veteran Member
Joined
May 30, 2016
Location
Nashville, AR
TDI
2001 Jetta TDI 2000 Jetta TDI 2000 New Beetle TDI ALL 5 speeds
There was talk of metal nerd making one you could use in place but it just seems like a bad idea, I've had a few that the triple square bit needed a little tapping to get it seated...hard to do in an already cramped space

Sent from my Pixel XL using Tapatalk
 

Dhawk12

Veteran Member
Joined
May 21, 2018
Location
Langley, Canada
TDI
2002 ALH 5 spd
If for whatever reason changing the pulley doesn't fix the problem, next place to look would be the voltage regulator. My light started flashing randomly one day, then almost immediately the cluster started going nuts (Speedo and tach fluctuating wildly, multiple lights flashing). Pulled over and checked voltage, was producing 18 volts at idle. Unplugged it and fiddled with it and somehow got it to stop, only producing like 12.9 volts so I could limp it home on back roads while monitoring voltage from obd. Pulled into the driveway, popped the hood to do more investigation, and the alternator burst into flames before my eyes.

Sent from my Pixel 3 XL using Tapatalk
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
I'd start with all the big wire connects,battery, alternator, whatever feeds the cluster/ignition.
 

csstevej

Top Post Dawg
Joined
Aug 12, 2004
Location
north nj
TDI
2001 golf tdi 4 door auto now a manual, mine, 2000 golf 2 door M/T son's,daughters 98 NB non-TDI 2.0, 2003 TDI NB for next daughter, head repaired and on road,gluten for punishment got another tdi 2001NB,another yellow tdi NB
It can be done in the car, I’ve done several of them.
I’ve yet had to pull the alt just to change the alt pulley.
 

steve6

Veteran Member
Joined
May 25, 2010
Location
Beaverton, ON
TDI
2003 jetta tdi
So about 3 hours total to get the alternator out and on the bench and re-installed.
3 hours is a lot.. I've changed them in under an hour. A/C compressor drop, Fan removal, remove belt, unbolt tensioner and then alternator, a few wires, wiggles on out.
 
Last edited:

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
In post #1 OP says As for the alternator pulley, it spins only counterclockwise when I put a screwdriver into the housing. I am met with a little bit of resistance, enough so it stops spinning as soon as I remove my hand.
Isn't that how it's supposed to work? (never had to mess with it). Some have had issue with the B+ wire to the alternator. Connectror, even the wire corroding inside.
Check the ground wire on top of the transmission.
 

WildChild80

Veteran Member
Joined
May 30, 2016
Location
Nashville, AR
TDI
2001 Jetta TDI 2000 Jetta TDI 2000 New Beetle TDI ALL 5 speeds
In post #1 OP says As for the alternator pulley, it spins only counterclockwise when I put a screwdriver into the housing. I am met with a little bit of resistance, enough so it stops spinning as soon as I remove my hand.
Isn't that how it's supposed to work? (never had to mess with it). Some have had issue with the B+ wire to the alternator. Connectror, even the wire corroding inside.
Check the ground wire on top of the transmission.
I've had one that felt good even twisting and stopping in a ratcheting motion but it wouldn't work right when it was in the car...both of my clutch issues came after the car sat for a while

Sent from my Pixel XL using Tapatalk
 

rallywagon

Veteran Member
Joined
Sep 19, 2007
Location
Western NC
TDI
'98 Jetta, '00 Jetta
LED lights in the the rear brakes / turn signals can cause the glow plug light to come on sometimes.
 

cygnus

Well-known member
Joined
Apr 7, 2014
Location
nova scotia
TDI
2000jetta, 2001 jetta doa ,2002jetta 2006 jetta wagon
I have had broken alt wiring under battery box at the connector and only got proper voltage when revs were up.
Could see it jump across the broken wire.
 

Fahrvegnugen

Veteran Member
Joined
Jan 21, 2017
Location
Burlington Vt
TDI
01 golf 1.9 alh gls silver
I’d just replace the tensioner and belt to stop the squeaking. Also clean under battery grounds and big wire ends to alt. Sounds like pulley is working. I’d only spend the time doing the alt pulley in car if I had more time than money and possession of the specialty tool. My pulley replacement appeared working but alt died within 6 months and left me wishing I’d just replaced the thing the first time. One day It had a metal grating sound then sounded like a bolt flew off and then it was fine for a time, until it stopped charging.
 

hey_allen

Veteran Member
Joined
Nov 25, 2006
Location
Altus, OK
TDI
2000 Jetta TDI
Mine wasn't the fastest thing to change, but I did it in the car as well.
Using the metalnerd tools, and being sure to force the tools fully into the splines, it came out without too much drama.

I did have to use a second wrench slipped onto the jaw of the first one to get the pulley broken loose, but that was the only bit of trouble.
 

spreadpanic

Member
Joined
Oct 6, 2015
Location
Baltimore, MD
TDI
2002 Jetta
So, to update! Ended up ordering a new tensioner and a new alt pulley. Decided to just do the tensioner first, since mine had a noticeable squeak and a little play.

When I got off the old one, I glanced at the alternator and realized one of the mounting bolts was loose. Went to tighten it, but it turns out it was sheered in half! Anyway, this seems like it could be the issue? With the broken bolt, alternator has slight play, so perhaps it has been bouncing off the belt, causing super brief drops in power that don't register on the multimeter.

Since it's the same bolt I'd like to procede with a propane torch, and hope to achieve what whitfield96 did in this thread. Problem is, I don't really understand the nature of this "puck" or what he means by press it out? Something I'm missing here? Is the accessory mount hole itself not threaded, and I could jam something in the passenger side hole to push the broken bolt out, with the puck, once it's heated? Cut, repeat?

Going to try shooting him a PM, but hasn't been active in a number of years.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
Never done this but I believe that thing is a sleeve that fits in the hole and mates to the block. One person said they couldn't get it off without breaking the alternator. Hope that's not the case, it is snug in there. Raising the motor seems like a lot, but will it give you the required clearance.
 
Top