jkcorradovr6

Hoping to get some insight on a charging / voltage issue I am having in my 2005 Cayenne S.

Here is a little background on my PIG. Purchased her three months ago (first Cayenne) with 133k miles and immediately started having an intermittent charging / voltage issue. Seems like I got hosed and smacking my head for not getting a PPI. I gave the vehicle a good look over, but somehow missed this issue. I was concerned with coolant pipes (replaced) and the more notorious problems that seemed to check out.

So I was optimistic and figured lets fix this issue. When I would first start her up in the morning everything would be perfect. Volt gauge would read 14v and everything functions normally. After letting the engine run for 15 or so mins, if I would shut the vehicle down and restart I would only get 12v out of the volt gauge, eventually the battery / generator light would become present on the gauge cluster and voltage would continue to drop. This would persist no matter how many time I shut off and restarted the engine.

Now if I let the car sit over night and start the next morning, voltage would be back to 14v until I shut the engine off and restart. The PO gave me a receipt for a new interstate battery that would be about 12-13 months old today and I would estimate about 3,000 miles of driving occurred since by PO.

Some things I did to try and remedy the issues were checking for loose connections on the battery and chassis grounds. Found none and clean each connection thoroughly.

I then read about water infiltrating the cabin and low and behold the diver's foot well was soaked after a rain storm. I cleaned the rain tray ports (DS was clogged) and let the foam insulation dry out for a week in the garage. I checked the wiring along this path where the water sits, but did not see any visual problems. I also peeled back the tape on the three spliced wires Porsche poorly did from the factory and all connections were perfect with no corrosion.

The next repair is where I am really kicking myself for miss diagnosing. I was under the impression that maybe I had a faulty voltage regulator. That would work when cold, but once heated up lost connection. The alternator was original to the vehicle. Since they are sealed units I dropped some money on a new alternator from Sonnen and installed.

Once in, I fired her up and gauge only went to 12v. I gave her some gas and boom right to 14v. Checked with a multimeter and I was getting 14.15v at jump terminals. I put the wheel liner back, let her run for 15 mins, went to get some gas and go for a ride. After restarting from gas station volt gauge only went to 12v and with some revving no change. Deciding to just head home as I was exiting the gas station the volt gauge went back to 14v. So I went for a 40 min drive that ended up being mixed highway / town driving. She performed beautifully, no issues, all electronics were operational, no dash lights, headlights came on when the sun went down, etc.

When I got back home, I shut the engine down and fired her back up to only see 12v again, revved the engine with no change, then received a battery / generator warning light within 60 seconds. Drove around the block and back to 14v on the volt gauge. Back to the drive way and repeated process to get 12v after restart and the same warning light. This time after a drive around the block there was no change. Let her sit over night and fired her up today and noticed something strange.

The car would always initially go to 12v on the gauge, but I would hear something engage or turn on in the engine bay moments after and the voltage would jump up to 14v. It kind of sounded like the fans kicking in. I don't think it was the air pumps, because the same thing would happen even at operating temperature.

As of today, I would have 12.2v with car off, 11.9v with engine running and 14.15v once up to "operational voltage output".

I am not an expert with wiring/electronics and hoping some members can give an insight on what to look for to fix the issue. I did lot of searching and can find similar situations, but none exactly like mine.

deilenberger

Very odd since the behavior changed significantly when you installed the new (rebuilt?) alternator. The first scenario was all was fine if started with a cold engine, if started with a warm engine - no charging. The second scenario is that cold or warm - the charging isn't occurring initially, but you hear something happening in the engine bay and suddenly you have charging. The obvious path to me would be to try to track down what's changing in the engine bay, then figuring out how that would change things so the system starts charging.

It is possible a rebuilt alternator could behave like you're describing.. if one of the brushes was hanging up and not making good contact with the commutator and the noise you're heading is the noise the alternator makes when charging at high current. I'm guessing the serpentine belt tensioner is working correctly and there is tension on the belt..?

Do you have a mechanic's stethoscope? Worth getting if you don't (Harbor Freight - $3.99 often on sale..)

jkcorradovr6

I initially thought that about the replacement alternator. The p/n on the alternator I received from Sonnen ended in 05 which from my understanding is the alternator that supersedes the alternator with p/n ending in 03 that was in my car. Though the p/n on the box of the alternator ended in EX and if I remember correctly that signifies a rebuilt unit. I couldn't imagine the updated p/n already out being rebuilt, but I'm sure there is something I am missing.

Serp tensioner seems perfect. It had a lot of pressure when removing the belt for the r/r of the alternator and has great belt tension when installed.

I didn't have much time to try and diagnose for the change in the engine bay after I noticed, but plan to start there next. I'll put a stethoscope on the alternator when the voltage kicks in to see if I hear any notable changes.

nodoors

Don is right, I would also try to get to the bottom of the sound you are hearing. Is it potentially that of electricity arcing and or the alternator making a clicking sound when the wiring gets continuity?

It is starting to sound like a wiring issue to me if you are not hearing your belt slip or squeal. Perhaps changing out the alternator and agitating the alternator wiring changed the (mis)behavior. I would start with checking your ground to your battery in the driver's footwell since you already mentioned you found water there. Then I would inspect the harnesses and cables at the alternator. There are two very well known issues in the 997 that cause a similar behavior to what you are experiencing:
https://rennlist.com/forums/997-foru...voltage-3.html

v10rick

When these things happen I always return to the source. Regardless of what the PO said about the battery have it load tested. There could be a cell on its way out.

CAVU

I have had similar issues with three alternators. All Bosch (240 Volvo and 450SEL Mercedes). In each case, one of the carbon brushes had worn down to point that it was make intermittent contact with the slip ring. In each case I soldered in a new brush and all was well. Or, one of the slip rings is worn down.

Not sure what the life expectancy of alternators are these days. At 100k, I get a little wary.

I do not know that the VR on your Cayenne is replaceable or fully integrated into the alternator. There appear to be aftermarket VRs that once the alternator is out, you can pull the VR and look at the brush lengths. Certainly an inspection of the slip ring would be in order too.

Good luck.

jkcorradovr6

Thanks for the input everyone.

I had sometime to work on it this morning and found some interesting results. Since I already threw a new alternator in, I thought I should test wiring.

I checked for continuity on alternator cable and junction box in engine bay...all was good. I then checked to make sure the exciter wire was getting 12V. It had 9.8V with the ignition on. Then I figured let me start her up and make sure the exciter had 12v while running. Results were 12.2V.

Now here is where it gets interesting, while testing, I noticed the volt gauge on the cluster was reading 14V with the exciter wire unplugged! I checked the engine bay terminals and it matched at 14.2V I shut her down and plugged back in the exciter wire and the problem resumed.

Long story short after starting and restarting multiple times and a quick drive over the course of 45 mins, I was getting perfect voltage and no issues with the exciter wire unplugged.

I went to a local alternator/starter repair shop (that's all the guy does and has been in business for almost 40 years) to tell him my situation. I explained the back log as mentioned above and he was perplexed. He asked for the VIN and he was able to look up the type of alternator it was and how the system worked. He told me there is nothing special about it compared to any normal car on the road. He has seen some alternators come in that are computer controlled, but this is nothing fancy (I said besides the watercooling).

He said many voltage regulators are self exciting and it looks like this could be the case with mine. He said to probe the exciter plug (give it 12v) while vehicle is running and volt meter is on terminals and see if there is any change.

Anyone have any ideas or know where I can find a complete schematic of the exciter wire?

oldskewel

This is for a 2004 S, and is the circuit around the alternator, not internal to it. But maybe it helps.

jkcorradovr6

Thank you!!!

Bodymotion Inc.

Just curious if you ever solved this problem

Jason D. Sharp

Mine has 285 k miles, I just unplugged the exiter wire cause it only had 10 v running and it now charges 14.06 volts and it fixed my brake lights that were dim. And turn signals. So why does it even need this exciter wire if it’s self exciting, I’ve Been running mine not hooked up and problems solved.

Greg Morey

Hey Jason, This seems like a common problem. Any further issues after removing the Exciter wire?
I'm having that same issue but I don't know where the exciter wire is or how to find it yet.

- Greg

Jason D. Sharp

No issues at all. Totally solved the issue, wire is located right on top of alternator on passenger side of engine towards front down low. Pull upper snorkel off and somewhat simple access. I will continue to drive it like this until it becomes an issue I suppose.

wraunau

Hello, I have a 2004 Cayenne S and cannot find the exciter wire. Would you have a picture? Thanks.

Jason D. Sharp

I don’t have a pic but it’s a single wire with a connector very close to alt, if I can recall it’s a blue wire but it’s been so long since I’ve pulled it loose. It should be tucked into harness, the wire had low voltage, like 10 v, something is causing the wire to have low voltage and I would guess the low voltage is causing alt or generator to not excite. I am curious what the wire is for other than to softly excite alt so it doesn't have to rely on rotation to start charging, that actually may be the only reason for the exciter wire hence the name lol. I thought about running a jumper wire but there’s a reason for low voltage. A module mabye?