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Discussion Starter · #1 ·
Hi Everyone,

I searched before posting and could not find anything that sounded like my issue.

When I accelerate and the RPMs climb above 4,000 RPM, my voltage gauge starts to drop and the system appears to cease charging. It will resume charging if I fall below 2,000 RPM. Any idea what is causing this before I start throwing parts at the car?

Thanks!
 

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1) Battery? how new?
2) Voltage regulation? A part of the alternator - brushes? bench test?
3) And most important - what does VCDS readout say?
 
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Belt going slack at higher RPM?
 

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Discussion Starter · #4 ·
I am not sure how old the battery or voltage regulator is. It sounds like replacing both might be a good place to start. I haven't checked what VCDS says yet. What should I check in VCDS; Voltage?

1) Battery? how new?
2) Voltage regulation? A part of the alternator - brushes? bench test?
3) And most important - what does VCDS readout say?
 

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the electronics realize you need all the power possible to the wheels so the alternator and other unnecessary ancillaries are disconnected in order to deliver max power to the transmission.
 

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Discussion Starter · #7 ·
I don't think that is the case here. If I do not let the RPMs fall below 2,000 RPM, charging will not resume and after a short while I Will get a message on my cluster telling me non-essential electronics are being shut down.

the electronics realize you need all the power possible to the wheels so the alternator and other unnecessary ancillaries are disconnected in order to deliver max power to the transmission.
 

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If your belt tension is good, then the alternator is probably going bad. I doubt you can "rebuild" the newer ones (far more complicated than a GM 12si....) so they will simply replace it.
 

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Okay didn’t want to make a new thread. OP you’re problem is very similar to mine.


2004 V8 fully loaded keyless entry air suspension towing etc. it was a one owner with 150k miles and very clean. Since I own a Phaeton thought it would be easy to track this voltage issue down. Owner was up front about it and I honestly figured one of the following would have fixed it..... it hasn’t and I’m at my whits end finding the source of the problem.

I have replaced the Alternator
Replaced the B+ battery cable.
Replaced the positive jump post
Replaced engine ground wire
Removed all ground wires (two in passenger plentium / two under passenger frame rail near SAP / and two grounds on each footwell inside.
Removed carpet on both sides and inspected wire looms for splices. (Re connected all splices with new connections just Incase )
Brand new battery
New air compressor
New air compressor relay
New serp belt
Rebuilt Kessy with new MOSFET chips and tested all resistors
Removed all major fuses cleaned contacts in fuse box in engine bay. Driver dash and passenger dash and all connection points under driver seat.


There are 0 faults present until about 1 hour into driving.

I can hear relays start to click and you start seeing the low voltage errors start popping up one by one effecting modules furthest away from the battery. Eg trailer , air suspension control module. Rear diff etc. headlights flicker too and if really bad fuel cap / large evap leak. Intermittent cat bank two. All codes are sporadic and never show if voltage stays at a normal range.

However resting voltage is 12.9
Idle voltage is 14.1

If rear windshield heater is on with stereo, headlights, fog lights , all 4 heated seats you get 14.5 volts at the cig plug inside and at battery terminals, positive post in engine bay etc.

But once the car has been driving for a bit you start to see the voltage hover around 13.9 then around 13.8 is when the faults start to appear.

Is there anything I missed ? I’ve been working on this for a month now.


I also replaced the following items before I knew that this electrical issue wouldnt go away.


Rebuilt transmission
Timing belt
Timing chain cam solenoids both banks
Valve cover gaskets
All vac tubing for egr to intake flaps
Cleaned intake manifold
Removed carbon build up on intake valves
New spark plugs
New coil packs
New 02 sensors x4
New cats
New brake vac hoses
New power steering rack
New upper and lower control arms front and rear
New brakes front and rear
Rebuilt both front and rear diffs with new fluid
Cardin shadt / carrier bearing
New rear drive line
New level sensors x4
New tpms sensors
New xenon ballasts
New xenon bulbs

So now about 15,000$ in parts and countless hours on my part I now have a perfect paper weight...
 

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My only other idea is another relay is bad only after it gets warm?? Took a IR temp gun and the warmest relay under the hood was the 167 which I was under the impression was for the fuel pumps ? Though I’ve had 0 issues with starting etc.

Btw worth mentioning. Touareg sat in the garage for two months battery dropped down to 12.5 I checked the level before starting the car and it started just fine. So I don’t believe there is a drain
 

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2006 V8 Touareg AIR, nav, hid
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It would seem that almost everything has been changed. :(


clubtouareg.com/forums/f43/voltage-troubles



See the Touareg SSP 298 for how the charging system works.

Also re-check battery ground and check the ground near the alternator. Both have been know to go bad.

Swap the battery if they will let you. Beg them for a loaner battery for a diagnostic test drive if they won't exchange the battery. You just need to confirm that the battery is good for one drive with a battery swap. If nothing changes...

Change the alternator again.
 

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Battery grounds are all fine. And the battery is a brand new agm. My friend runs a parts store. I’ve killed 4 battery’s this year trying to find out. My only other guess is relays a module or wire damage some where.

I’ll check into the ssp thank you. I really really wish the Touareg had a battery charging module like the phaeton. Easy access and cheap to swap lol
 

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The ground near the alternator has a new cable already btw and everything is OEM.

The alternator is not the issue it’s new not refurbished and I’m never shucking out that kinda money again for another one.
 

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Safe to say it’s not a charging issue it’s a short from a unwelcome guest ... wasn’t like that when I bought it. I cleaned out the rear cargo area. Auto part Vehicle Audio equipment Automotive wheel system Car
 

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Interesting, I had the exact same symptoms leading up to my complete failure.
Albeit mine is a V10 and mine dropped voltage at 2000 RPM and recovered at 1000 RPM.
 

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I pulled the whole cargo area out. The mouse stayed in the cargo area. It never ate any wires. Going to pull all the door sensors for keyless entry and see if there is a very small drain perhaps ?
 
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