Periodic random electrical shutdown

Its a 2006 jetta tdi with about 280k miles. Happens only when driving. It started doing this a little after i had a minor rh front collision with a big concrete barrier. The engine and all lighting is unaffected. But all of a sudden there is a shutdown of the electrical systems. The instrument cluster turns off, airbag and brake light comes on, power steering is lost, car shifts itself into neutral (i suppose because the mechatronic control shuts down). After 1 to 5 minutes, all turns back on. Thinking the collision had jarred some main power connector loose, i purposely drove it over the biggest potholes i could find. Did not induce failure.
I read out all fault codes with vcds. Nearly every controller is registering a bus overvolt. One fault registered says over volt at terminal 30....wherever that is. The amount of overvolt sensed is 17.4 volts. I got a 12v dual usb outlet adapter with voltage readout and it shows a steady 14.1 volts. Do the controller ecu's have have ovp circuits that shut them down above a certain voltage? What could be the source of high voltage glitches? guess i have to try a new alternator?. Can i obtain and rdplave only the regulator?

Cannot say I have ever run into a situation where a Bosch alternator was OVER charging, and I assume that because the issue was not present before your crash that the alternator even if it is a low grade aftermarket replacement is not the cause.

Some things to check:

Connections at the main fuse link bar, which is attached to the front of the underhood fuse box, look for any signs of corrosion, rust, loose connections, or hot spots.

Connections UNDER that same underhood fuse box (which to check generally requires removal of the leads coming from the fuse links mentioned above, then you simply remove the single Torx fastener in the center of the box and pull it up and off). Check for any green corrosion under there.

Check the ground points, starting with the battery ground at the strut tower, then going down to the grounds on the body under the air cleaner (one is down low, that is the ground for the power steering and the main strap to the engine/transmission, the other more over on the inner fender is for some other lower amperage items).

Also, did the repair that was made involve any welding? This can cause ALL SORTS of bad things on cars if the electrical system was not isolated properly during the repair. Which most body shops are not good about doing because it involves too much work (and most body guys know as much about automotive electrical systems as I do about tampons).

Let us know if you find anything.

It was the right front wheel/rim and tire that actually struck the concrete barrier. There was a huge jolt to the whole car, but only wheel/rim was damaged. No repairs were done to the car itself.
It was right after i changed the damaged rh front tire for the spare, that this first electrical momentary shutdown occurred. Just a few miles down the road.
The first thing i thought was that the shock had loosened the main engine fuse box connector. So i loosened the torx screw , pulled off and checked for any problem. It was fully secured and no corrosion. And after doing that the intmt. Failures continued
I had thought its an intmt power bus failure from a connector jarred loose by the impact.....but i dont know of another connector besides that one i already checked that could kill so many systems together. Then i checked vag com codes and i'm thinking: could the controllers be shutting off in reaction to a brief over voltage glitch caused by faulty volt. regulator? I dont know if they have such over voltage protection or not. I need to know where that terminal 30 is. But it seems that nothing could output an over- volt glitch except the alernator regulator, right?

I would not rule out charging issues. That's where I would start, there are several things that could cause that.
1. Alternator regulator
2. Alternator rectifier
3. Intermittent loose connection at the alternator
4. Intermittent loose ground connection.

The alternator regulator and rectifier are fairly simple problems, I've seen a lot of over charge issues, and even with Bosch, though they are normally pretty good. Now, if the alternator has been replaced with a non oem one (parts store brand) then that is even more common. One of the most surefire ways to test them is with an oscilloscope. Though not everyone has access to one of those.
I am an electrical rebuilder, I rebuild starters and alternators and so I have seen a lot of ways they can fail. I also can get the Bosch rectifier and regulator for these alternators, and so if you determine that is your problem, I can help you out.

The intermittent power and ground can cause voltage spikes because the alternator thinks its not putting out voltage, so it'll ramp it up, whereas it actually was and it will over charge.
So, check all power and ground connections you can.

I'd recommend pulling the alternator voltage regulator which has the brushes attached to it and look at the brushes too. If they are getting short then it can arc across which will also ramp up voltage. Also check how much AC voltage is being put out. That's where an oscilloscope is really handy, either that or a true rms multimeter. You can also take the alternator to be tested at many auto parts stores and they should be able to tell you how much AC or ripple voltage there is.

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This car makes 60 mile commutes daily. The eletrical outage sometimes doesnt ocvur at all on a days commute, and it has almost always been only one incident. One either going to or from work. I doubt a mechanic shop would find anything. I am kind of electrical handy, and i am kind of ham strung on repairing it.....since its always working fone running at the house. If it would fail and stay failed i could run it down. I have a scope, dont think ill see the glitch while i have it connected up. I could replace the alternator with a reman from oreilly for 130.00 plus core....but would much rather replace regulator only if i can find a supplier. Replace and see how it runs then. thanks, jim

The O'reilly alternator will be a piece of garbage. Which is why I would want to know for sure that the alternator has not been previously replaced with such. Bosch reman is the only way to go, although you can certainly get an OEM Bosch regulator/brush set and replace it for less if you want to try that.

Again, never heard of a Bosch one doing that, but I assume it is possible. Look on the back of the alternator and see if it does actually say Bosch on it, and has the little white tag. Or post a pic if you like.

jimigunne said:

This car makes 60 mile commutes daily. The eletrical outage sometimes doesnt ocvur at all on a days commute, and it has almost always been only one incident. One either going to or from work. I doubt a mechanic shop would find anything. I am kind of electrical handy, and i am kind of ham strung on repairing it.....since its always working fone running at the house. If it would fail and stay failed i could run it down. I have a scope, dont think ill see the glitch while i have it connected up. I could replace the alternator with a reman from oreilly for 130.00 plus core....but would much rather replace regulator only if i can find a supplier. Replace and see how it runs then. thanks, jim

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Good, you have a scope. That's even better! Look at the ac waveform. It should be below 0.5 volts ac on the highest spike. Also, the ac or dc waveform should be even without spikes or static.
I would recommend against an OReilly alternator, even though they have a lifetime warranty. My recommendation would be either Bosch or Valeo, or rebuilt with Bosch parts.
I can get you a regulator in the Bosch. It's a bit pricy, but not as much as a new alternator, though if it's the 110 amp one, it's cheaper. I sent you a message via forum pm.


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Well this is definitely crash related! I do think i replaced the alternator around 3 yrs ago....im thinking it was an autozone reman, but have also bought alternators from Rock Auto. For sure its not genuine Bosch brand.
I just checked electrical connector to alternator and it is still tight and secure. I am clueless how i could check ac waveform since its rectified from ac to dc internally. I guess you mean the ac component riding on the dc output. Monitoring right at pos. battery terminal the voltage is exactly 13.7 and very stable. (And yes my fluke is true rms) I installed a scangauge on the dash using the diagnostic port so the system voltage is constantly displayed.
If it is a momentary high voltage glitch ....like from 13.8 volts up to 17.4....and its being driven at night, i would think it would be apparent in a sudden brightening of the headlights.

jimigunne said:

Well this is definitely crash related! I do think i replaced the alternator around 3 yrs ago....im thinking it was an autozone reman, but have also bought alternators from Rock Auto. For sure its not genuine Bosch brand.

I just checked electrical connector to alternator and it is still tight and secure. I am clueless how i could check ac waveform since its rectified from ac to dc internally. I guess you mean the ac component riding on the dc output. Monitoring right at pos. battery terminal the voltage is exactly 13.7 and very stable. (And yes my fluke is true rms) I installed a scangauge on the dash using the diagnostic port so the system voltage is constantly displayed.

If it is a momentary high voltage glitch ....like from 13.8 volts up to 17.4....and its being driven at night, i would think it would be apparent in a sudden brightening of the headlights.

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What brand scope do you have?

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Tektronix 30 mhz dual trace . its an old CRT scope i got for cheap on ebay but still works good.

I have a portable scope coming in a couple of weeks. If i had that i could connect via 12v dc jack and a passenger assistant could monitor and maybe see a glitch. Unfortunately its not going to be a dso.

jimigunne said:

Tektronix 30 mhz dual trace . its an old CRT scope i got for cheap on ebay but still works good.

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Ok, I've never used that one, I have a picoscope. Basic principal will be the same. Connect to positive and ground at alternator, if your scope will do ac current, set it to that and watch the waveform.
https://forum.allaboutcircuits.com/threads/oscilloscope-analysis-of-alternator.132148/
Here's a basic overrun of it.

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Alternatively, being that you have a fluke... Switch it to ac current for about 2 volts ac. Connect that to the back of the alternator while the car is running and see what the ac voltage reading is. That's not quite as accurate, being that you can have a failed diode without too much ac voltage, it'll just show up on the waveform.

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AC voltage bleed over used to be very common on Delco/Delphi alternators. I remember seeing that a lot on GM stuff way back when. GM largely uses Bosch or Denso units now.

But yeah, electronics do not like AC voltage flopping around on the lines. It wigs out 5v reference sensor signals, although that does not sound like what you have here (still, if it is an Autozone alternator, that is where I would start).

Yea.....i'll scope the dc output sometime this weekend. My son just drove it 30 miles to next town and back, and never the slightest glitch the whole trip. Tnx.

Yes it was indeed a faulty alternator. Replaced and no further occurrences. Thanks guys for your input.

Just FYI, whenever any car comes in our shop with some strange electrical malady, possibly including but not limited to the battery and charging system, and I see a non-OEM grade of alternator, I immediately investigate that. And 90% of the time, that is the problem.

On these cars, if it is not a genuine Bosch unit, it WILL fail and cause problems. Guaranteed. Sometimes for a lifetime.

jimigunne said:

Yes it was indeed a faulty alternator. Replaced and no further occurrences. Thanks guys for your input.

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Funny thing is that I had someone bring a unit in the other day, though it was a Ford, but they said it wasn't starting very well. The battery was at 1.3 volts. I jump started it and checked the voltage, it was fluctuating between 11 and 27 volts. I then checked the rectifier, and it was shot, it was putting out several volts ac. It was telling the rectifier to put out more charge, and so from the DC side, it looked like a simple overcharge, but the AC side showed why it was overcharging. I did a complete rebuild and replaced the battery, and it was good.

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