No Battery Light, car not charging

Hi:
I've got a 2001 Jetta TDI with 90k miles. Earlier in the week I was driving home and my battery light came on. When I got home I verified that the battery voltage was low and that the the charger didn't appear to be working (voltage staying at about 11.3 at any RPM). Since then, I've been driving about 20 miles a day with the headlight fuses removed and recharging the battery at night. Now, I want to fix the problem.

I have verified that I've got battery voltage at the B+ (big) alternator terminal, and on both the contacts inside the little connector on the alternator.

BUT: My dashboard battery light does NOT come on when I turn the key to the 'run' position (i.e. with the car off, I turn the key to 'run' and all the other dashboard indicators come on, but there is no battery symbol). The Bently manual indicates that this suggests a wiring problem that should be fixed first, but aside from verifying battery voltage at the 3 points on the alternator, it's unclear what could be wrong or what should be done.

So, my first question is, would a bad alternator/regulator keep the light from coming on? I really don't want to go the the alternator R&R procedure if I've got some other problem.

Thanks for any diagnostic suggestion,
Phil

PS: I did take it to Autozone for a diagnostic and they confirmed that the alternator wasn't working, but could offer no other guidance.

The BAT light is actually an important part of the charging circuit... it's how the alternator gets the excitation voltage it needs to begin generating electricity on its own. No BAT light, no charging!

What's a bit strange is that it sounds like your BAT light was working (ie it came on while you were driving) but no longer does?

In any event, gotta get it working. The most usual (non-alternator) issues are with the connector at the back of the alternator, the wiring between the alternator and the cluster, or the cluster itself... and kind of in that order.

One possible set of troubleshooting steps:

1) Start by unplugging the harness at the back of the alternator and inspecting carefully... any corrosion? Broken/loose wire?

2) If not, you'll need your Bentley to find out which terminal on your particular harness is the D+ lead... this is the one that goes to the BAT light. If you ground that lead and turn the key to "ON" the bat light should come on. If so the wiring and cluster are fine and the problem is most likely internal to the alternator... the voltage regulator being the usual suspect. If the light doesn't come on the problem is the connector, the wiring, or the cluster... the bulb itself is an LED and almost never burns out.

Vince:
Thanks for the advice. The Bentley schematic said that pin 1 was D+, so I grounded it and the dash light came on. So, I guess it's time to replace the alternator.

-Phil

Many auto part stores will check the charging circuit for free. If have have enough of a charge to get to one and back, you might as well have them check it. The price is right.

Joe_Meehan said:

Many auto part stores will check the charging circuit for free. If have have enough of a charge to get to one and back, you might as well have them check it. The price is right.

Click to expand...

Joe: As I said in my original post, I did that and all they could do was confirm that the car wasn't charging.

oops

jcrews said:

Trace the signal back to pin 2 on the 4 pin starter connector.

Click to expand...

jcrews:
I don't quite understand what you want me to do/check here: haven't we essentially verified that the wiring is OK? I've got battery voltage at the alternator (on the B+ and D+ connectors) as desired, and *if* D+ is grounded, then my battery/charging indicator light comes on.

Sorry, I had a moment. If you get battery voltage at D+, your regulator is probably shot. Remove the regulator and make sure the rotor coil isn't open.

I put the Vag-Comm on it and got the code:

17911 Load Signal from Alternator Term. DF: Implausible Signal
p1503 - 35-10 - - - Intermittent
Readiness 1 1 0 0 0

Should I assume that, in light of this most recent piece of information, I should continue with alternator replacement?

-Phil

Yes, but a regulator is cheaper so long as the bearings and coils are OK.

Chances are that the issue is the regulator... but before you buy one pull the old one and then have a close look at the commutator.

If it's got much wear it will eat the new regulator/brushes in short order... BTDT.

Also bought one once before checking... found the wear as I was putting in my new, non-returnable, now useless regulator!

If you go the "new" alternator route, you should take a look at a Pep Boys near you. I got a remanufactured Bosch alternator for $169 out the door, and it includes a lifetime warranty.

They had two 120amp reman. alternators: a Bosch and a Hitachi. You should ask to look at the Hitachi alternator and see what's in the box. In my case, it was a Bosch reman., but I still paid the cheaper Hitachi reman price. If it looks identical to your Bosch alternator (assuming you have one now), then you are good to go. If not, ask to look at the Bosch reman. one.

jcrews said:

Yes, but a regulator is cheaper so long as the bearings and coils are OK.

Click to expand...

The Bently states that the 2001 model year alternators don't come apart, and that if the regulator fails, the entire alternator must be replaced, so...

I got the 120 amp rebuild with lifetime warranty from Autozone ($175), had it put in and all is fine now.

-Phil

Despite what the Bently sez, I see that Autozone *does* sell a replacement regulator (with a 3 month warranty) for $174!! (see http://www.autozone.com/autozone/catalog/parts/partsProduct.jsp?itemIdentifier=263898_40638_0_&skuDescription=Duralast+/+Voltage+Regulator&brandName=Duralast&displayName=Voltage+Regulator&categoryNValue=15799999&sortType=&store=967&isSearchByPartNumber=&fromWhere=&fromString=&itemId=prod61242&navValue=15700097&filterByKeyWord=&productId=263898&appQuestionText=&searchText=&categoryDisplayName=&parentId=cat30065&questions=[])