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Battery / Alternator Question

shade

Active member
Joined
Aug 17, 2011
Location
New York
TDI
VW Jetta TDI 2005.5 115,000 miles
During the early spring here in NYC my car sat unused for most of the time due to quarantine. I was able to jump start it with my portable battery, but for the first couple of weeks I had to keep jump starting it. Currently it is starting without any problems. Thinking I needed a new battery I stopped by autozone to have the battery checked out. The guy there said I need a new alternator.
So I did some readings with a multimeter (please keep in mind I am a beginner when working on cars.)
The car sat for about 3 days and before starting it the battery read 12.5
Once started and idling it read 14
Revving the engine moved it up above 14 by a few points.
There is no battery warning light or anything like that coming on.
Is there anything else I should do to determine if I need a new alternator or battery?

It's a 2005.5 VW Jetta TDI with about 114,000 miles.
Thanks
 

redbarron55

Veteran Member
Joined
Jul 10, 2010
Location
Navarre, FL.
TDI
2012 Touareg TDI Executive
Sounds like the alternator is working to me. It might go higher as high as 14.5 but the 14 v + will charge the battery.
12.5 was about a 80% battery, but might not be good enough for glow plugs and starting.
Keep checking before replacing the alternator.
Sometimes the alternator testers actually read the AC component of the DC to detect the possible bad rectifier in the alternator.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2005 BEW Wagon
You've done the right tests to confirm your charging system is working: a jump in voltage to around 14V once the car is started.

This narrows it down to a weak battery (most likely) or a current drain.

To properly test the battery you need a battery load meter; the Autozone that tested your alternator will have the right equipment to load-test your battery as well... although given that they are telling you you have an alternator problem you might want to find another Autozone and have them specifically load test the battery.
 

RabbitGTI

Top Post Dawg
Joined
Jul 20, 1997
Location
Wisconsin
TDI
B4 Passat Sedan
charging system is fine. You could test for a drain when the car is off, but I doubt if you have that. I would just get a new battery before you get stranded. How old is the battery?
 

shade

Active member
Joined
Aug 17, 2011
Location
New York
TDI
VW Jetta TDI 2005.5 115,000 miles
charging system is fine. You could test for a drain when the car is off, but I doubt if you have that. I would just get a new battery before you get stranded. How old is the battery?
The battery is about 4 years old. For now I never go anywhere without a fully charged jump starter. I found a small portable one that actually works on the diesel engine.
 

Jetta_Pilot

Top Post Dawg
Joined
Apr 14, 2005
Location
West Hill, Ont. Mexico mid October 2019 to end of
TDI
2015 Passat Highline TDI Candy White (SEL Premium) gone 2002 Jetta TDI
The battery is about 4 years old. For now I never go anywhere without a fully charged jump starter. I found a small portable one that actually works on the diesel engine.

A couple of years ago my Passat would not start. Bought the ONLY available set of booster cables but they could not move the starter to turn over the engine and fire up. A friend came to assist and he also had booster cables. Both sets were too small a gauge to start a Diesel.
Then I remembered reading long ago to use two sets of booster cables at the same time. Effectively it increased the amperage available. That WORKED for me.


My question to "Shade" is where did you find this jump starter???
 

SilverGhost

Veteran Member
Joined
Mar 25, 2005
Location
Back in So Flo - St Lucie
TDI
'05 Golf - totaled :(, wife's '13 Beetle - buy back, TDIless
@Jetta_Pilot - I have a NOCO GB70 that will start a dead TDI in most cases. LINK

To the OP - in the past about 17 years as VW dealer tech I can count on one hand how many alternators I have replaced. Most were for other reasons (I broke the mounting ear off one) and not due to internal failure or worn out.

That said - If you have to jump start a car, don't run the engine to recharge the battery. THAT will shorten the life of the alternator. Two things - if the battery is getting worn and tired then you will shorten the life of the starter and alternator. Both are way more $$$ than properly recharging or replacing the battery.

Also I have seen plenty of "failed" alternators that were just weak batteries. The same alternator promptly passed the same test with a good battery. Food for thought

Jason
 

shade

Active member
Joined
Aug 17, 2011
Location
New York
TDI
VW Jetta TDI 2005.5 115,000 miles
@Jetta_Pilot - I have a NOCO GB70 that will start a dead TDI in most cases. LINK

To the OP - in the past about 17 years as VW dealer tech I can count on one hand how many alternators I have replaced. Most were for other reasons (I broke the mounting ear off one) and not due to internal failure or worn out.

That said - If you have to jump start a car, don't run the engine to recharge the battery. THAT will shorten the life of the alternator. Two things - if the battery is getting worn and tired then you will shorten the life of the starter and alternator. Both are way more $$$ than properly recharging or replacing the battery.

Also I have seen plenty of "failed" alternators that were just weak batteries. The same alternator promptly passed the same test with a good battery. Food for thought

Jason
Thanks for the advice. The autozone guy kept telling me not to replace the battery even though I wanted to. So irritating. I will get it replaced the next chance I can. Thanks.
 

Tdijarhead

Top Post Dawg
Joined
Nov 10, 2013
Location
Lawrenceville PA
TDI
2003 TDI Jetta Daughters Car, 2001 TDI Beetle, Daughters car, 2005 Golf TDI Mine, all 5 spds
A charge of 12.5 is fine that should start your car every time. The problem is that the battery may not be keeping and holding a charge. When you were having issues starting, after the initial jump start were all of your trips short? If so the alternator may just not have had enough time to fully charge your battery.


12.2-12.4 is an weak/ok battery, 12.4-12.5 is a good battery 12.6-12.8 is a fully/freshly charged battery. Below 12.2 is a dead battery. 14+/- Is perfect for your alternator.


Keep in mind that Autozone would like to sell you a battery, alternator or both for that matter.
 

tdiinsc

Active member
Joined
Feb 28, 2018
Location
Greenville, SC
TDI
2015 Golf Sportwagen TDI, 14' Jetta TDI
I had this very same problem. Since i thought there was a chance that my battery would be covered under a warranty since it was less than 2 yrs old, i took it to my local dealer (my CPO paperwork said they replaced the battery). Turns out batteries arent covered under the CPO warranty that i had, but it could have been under the new car warranty which i was out of. Anyhow, i drive my car at least once a week during quarantine for 35 or so minutes, so you would think that would be sufficient, but id have the battery die the very next day after those drives. Dealer load tested my battery and said it was bad, they were happy to charge me for a replacement. In the paperwork they said the charging system was fine and was showing 13.8V (unless that was a typo, id expect it would be at least 14). Under their specs, they wrote that was okay. Lets hope i dont have to go back in a month for the same issue.
 

Mozambiquer

Veteran Member
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI
I'm a starter and alternator rebuilder, and have seen plenty of failures, but I've also seen a lot of parts houses claim that one is failed in order to make a sale (that's what they get paid for)
I've also seen it happen the other way.
So, your alternator is charging, but you can have an alternator be bad, even though it still charges the correct amount of DC volts if it has failed/failing diodes. That would be seen by the ripple volts (ac voltage) if it has more than .4 ripple volts, then it's considered failed, and it will cook the electrical system. That can also cause a battery drain. Now, a more precise test would be to use an oscilloscope to view the current flow and see if it is a nice clean waveform or if it has some voltage spikes in it.
Now, I know that many people have had problems with parts store alternators, so my recommendation if you need one, is oem or equivalent, (Bosch or Valeo)
If you must have parts store, get the reman, is actually better than their new ones.
 

ekincaid

Member
Joined
Jun 28, 2013
Location
North Carolina
TDI
03 Golf TDI
This is so very similar sounding to what I posted yesterday. When the car is running I see around 14 volts. The battery is brand new. Overnight it will completely drain. After checking the voltage on the fuses I am seeing 0.7 mV on the 150 amp fuse for the alternator. I did a diode test and it checked as good. But, once I disconnected the power from the alternator, no more drain overnight. Do you guys have any thoughts on this?
 

Mozambiquer

Veteran Member
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI
This is so very similar sounding to what I posted yesterday. When the car is running I see around 14 volts. The battery is brand new. Overnight it will completely drain. After checking the voltage on the fuses I am seeing 0.7 mV on the 150 amp fuse for the alternator. I did a diode test and it checked as good. But, once I disconnected the power from the alternator, no more drain overnight. Do you guys have any thoughts on this?
What diode test did you do? Was it testing for ripple current or testing for reverse flow? The simple way to explain how diodes work is that they are one way valves for electricity. If they aren't stopping backwards flow, they will allow the battery to drain, as well as they will allow backwards current to flow (alternating current, or AC) that will quickly fry your battery and can cause a lot of wonky electrical issues.
The way to test for backwards flow would be to use a multimeter (with diode test function is best) and with the alternator disconnected check for continuity from the positive terminal of the alternator to the negative terminal. There should be continuity one way and not the other. If you have the red probe on the positive alternator terminal, and the black one on the case, it should not have continuity, but vice versa, it should have continuity. Check that and let me know.
If you have the Bosch unit, a rectifier is available, not so for the Valeo. I've not checked for the hitachi one that a few of the mk4 cars have.
 

SilverGhost

Veteran Member
Joined
Mar 25, 2005
Location
Back in So Flo - St Lucie
TDI
'05 Golf - totaled :(, wife's '13 Beetle - buy back, TDIless
I had this very same problem. Since i thought there was a chance that my battery would be covered under a warranty since it was less than 2 yrs old, i took it to my local dealer (my CPO paperwork said they replaced the battery). Turns out batteries arent covered under the CPO warranty that i had, but it could have been under the new car warranty which i was out of. Anyhow, i drive my car at least once a week during quarantine for 35 or so minutes, so you would think that would be sufficient, but id have the battery die the very next day after those drives. Dealer load tested my battery and said it was bad, they were happy to charge me for a replacement. In the paperwork they said the charging system was fine and was showing 13.8V (unless that was a typo, id expect it would be at least 14). Under their specs, they wrote that was okay. Lets hope i dont have to go back in a month for the same issue.
Minor warranty black hole with batteries and NVLW vs CPO. Was the car still covered under NVLW when you bought it? Or was NVLM already expired and CPO in effect at time of purchase? Because batteries have their own warranty of 5 years prorated protection IF sold outside other warranties. I say this from experience of installing a battery a week before NVLW expired and a month later battery failed - no warranty. But if the battery was installed after the NVLM expired, then you still have some covereage.

Jason
 

ekincaid

Member
Joined
Jun 28, 2013
Location
North Carolina
TDI
03 Golf TDI
The way to test for backwards flow would be to use a multimeter (with diode test function is best) and with the alternator disconnected check for continuity from the positive terminal of the alternator to the negative terminal. There should be continuity one way and not the other. If you have the red probe on the positive alternator terminal, and the black one on the case, it should not have continuity, but vice versa, it should have continuity. Check that and let me know.
If you have the Bosch unit, a rectifier is available, not so for the Valeo. I've not checked for the hitachi one that a few of the mk4 cars have.
That is how I checked it. Sorry if I wasn't clear.

I've been doing a lot of reading to try to figure this out. But to be honest, am kind of clueless. The alternator is a Bosch.
 
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Mozambiquer

Veteran Member
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI
That is how I checked it. Sorry if I wasn't clear.

I've been doing a lot of reading to try to figure this out. But to be honest, am kind of clueless. The alternator is a Bosch.
Have you done a ripple voltage test? Many parts stores do that for free.
 

redbarron55

Veteran Member
Joined
Jul 10, 2010
Location
Navarre, FL.
TDI
2012 Touareg TDI Executive
Many digital voltmeters will read ripple when measuring using AC on a DC voltage. Mos of the Fluke meters I have tried will do this.
Also many times the brushes wear and sometimes the wire going to them gets tight and they won't make connection. If you have access to the field terminal check for continuity. Also a +12 volts on the brushes should give full output.
 

ekincaid

Member
Joined
Jun 28, 2013
Location
North Carolina
TDI
03 Golf TDI
Just got back from the parts store. They said everything checks out great on the alternator. So here is where I stand.

1. The battery (Brand New) drains overnight if I leave it hooked up.
2. I have checked every fuse multiple times.
3. The only fuse I can find a voltage reading (0.7 mV) is on S177 (150 amp) to the alternator.
4. When the cable is disconnected from alternator the drain goes away.
5. I checked the diodes with a multimeter and it was good.
6. Went to Autozone and was told it was working great after testing

What am I missing? Several people said what has changed on the car (i.e. new radio). Nothing has changed, before this started happening. If it was a new radio (or most anything else) I would think the draw would go through fuse S176 since that leads to the fuse box.

I truly have no idea where or what to look for. ?
 

Mozambiquer

Veteran Member
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI
Anyone have a thought?
So, I was looking at the wiring diagrams, according to that, the only thing that is on fuse 177 is the alternator. Now, when you disconnected it, which side did you disconnect? The black wire or the red wire? It's looking like you have a leaky diode, but it's not causing any other problems yet, just leaking backwards. I think that if you connected an oscilloscope to it, you may be able to see it in the waveform. So if you have access to one, that would be helpful, but not everyone does. I'm also thinking that you may have a battery that is getting weak. I don't know if you've checked that yet.
 

ekincaid

Member
Joined
Jun 28, 2013
Location
North Carolina
TDI
03 Golf TDI
The battery could be getting weak. I bought it new a couple months ago when this started happening. I have a really good electrical shop that has done work for me in the past about 30 minutes away. I think I'll give them a call and see if they can look at it. Thanks for the help.
 

ekincaid

Member
Joined
Jun 28, 2013
Location
North Carolina
TDI
03 Golf TDI
I'm sorry I didn't answer you question. I disconnected the black wire off the back of the alternator.
 
Last edited:

Mozambiquer

Veteran Member
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI
The battery could be getting weak. I bought it new a couple months ago when this started happening. I have a really good electrical shop that has done work for me in the past about 30 minutes away. I think I'll give them a call and see if they can look at it. Thanks for the help.
Main thing I would make sure of is if they replace parts, make sure they are genuine Bosch, not aftermarket. It'll cost a bit more, but last much better.
 
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