Alternator Workshop - Bad Alternator or VR?

db52282

Well-known member
Joined
Aug 25, 2010
Location
Georgia
TDI
2005 Passat TDI Sedan
Wife's 2005 Passat TDI (BHW) got the battery light and the Alternator Workshop notification (with the beeping).

Alternator pulley was replaced (new style) around 30K miles ago.

I have not determined whether I have the Valeo or Bosch alternator yet
but am leaning toward replacing the voltage regulator rather than the
entire alternator. The rebuilt units are VERY expensive.

Has anyone had the same problem and a voltage regulator replacement fixed the problem?

I read in the TDI 101 section that you should only replace the alternator if you have a bad bearing.

Any ideas or help is appreciated.
 

afarfalla

Veteran Member
Joined
Nov 6, 2006
Location
sugar land tx
TDI
05 Passat sedan and 05 wagen
get a voltmeter, set it to voltage, put the red lead to the bat positive, blk to the neg, read bat voltage, start the car, if the bat is weak the voltage should go up higher than the first reading, in any case the voltage should be around 13 to 14 volts, now turn on the lights radio anything that draws power, if the regulator is good the voltage should hold
 

thundershorts

Top Post Dawg
Joined
Jul 15, 2010
Location
west chester pa
TDI
2015 passat tdi sel premium 2015 golf s tdi gls tdi b5.5, 2002 eurovan,Peugeot 505 td,Citroen cx25 prestige
battery condition/age? Most auto stores will test your battery and charging system for no charge(pun intended)
 

db52282

Well-known member
Joined
Aug 25, 2010
Location
Georgia
TDI
2005 Passat TDI Sedan
I had the battery and alternator checked at the parts store. Battery age unknown.

Results: Battery tested good - 12.4v

Alternator: Failed - Producing 12.1v (Load or No-Load Condition)

Any additional advice?
 

Skivvies

Well-known member
Joined
Jun 10, 2006
Location
Westford, MA
TDI
2000 Golf, 2004 Passat Wagon
I had a similar problem, and when testing at the battery as suggested with car running I got less than 13vdc. The voltage would intermittently spike and the engine rpm would fluctuate in accordance with this spike (indicating the alternator was coming into and out of the loop), but for most of the time the voltage was below 13vdc. Pulley had already been replaced with new style but I checked the clutch mechanism anyway.
I replaced the voltage regulator and alternator output returned to normal. I would replace the regulator with one from the dealer (P/N 038903803EX). The cost was the same as online and it got to me in a day or two with no shipping charge. You can do it without removing the alternator.
I will add that at this time the battery looked like the original and a few months later it needed to be replaced. Whether it contributed to the failure of voltage regulator I don't know.
 

db52282

Well-known member
Joined
Aug 25, 2010
Location
Georgia
TDI
2005 Passat TDI Sedan
I would replace the regulator with one from the dealer (P/N 038903803EX).
Do you have a Valeo or Bosch alternator?

Is this part number the same for either the Valeo or Bosch?

Thanks for the information. I was heavily leaning toward replacing
the VR anyway.
 

thundershorts

Top Post Dawg
Joined
Jul 15, 2010
Location
west chester pa
TDI
2015 passat tdi sel premium 2015 golf s tdi gls tdi b5.5, 2002 eurovan,Peugeot 505 td,Citroen cx25 prestige
did they give you a printout of the system test? if the battery is original Varta I would consider replacing it with the vr or alternator. it might still test good in warm weather but may give troble when it gets cold
 

Skivvies

Well-known member
Joined
Jun 10, 2006
Location
Westford, MA
TDI
2000 Golf, 2004 Passat Wagon
Do you have a Valeo or Bosch alternator?

Is this part number the same for either the Valeo or Bosch?

Thanks for the information. I was heavily leaning toward replacing
the VR anyway.

alternator is a Bosch 120A P/N 028903031. This is printed on the backside of the alternator. You can give whatever alternator P/N you have to the dealer to find regulator P/N. The following site has all the info you need including the Valeo and Bosch regulator P/Ns:
http://www.myturbodiesel.com/1000q/b5/alternator-passat-removal.htm
 

Za786

New member
Joined
Oct 1, 2012
Location
Leicester
TDI
Passat tdi
04 Passat Tdi alternator workshop

Hi guys,

My alternator light came on the problem was the pulley was gone as when I turned the steering it would squeak.. After I got the pulley changed it was fine.
Now after a month i went to work every morning 30 mile journey each way and no problems but as soon as I returned home in the evening and switched the car off and on immediately the light came on.
Now from yday the light came on immediately and no problems on battery draining yet. The alternator is showing more than 13v
Does anyone know if it's the regulator? Where does that sit and how much is it?
Any help will be appreciated
 

abctdi

Top Post Dawg
Joined
Mar 31, 2004
Location
ABQ, NM, USA
TDI
2005 Passat GLS
Maybe new brushes will help?
When my pulley failed, I measured mine since they were easy to get to and they were still long enough.
 
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