We have had quite a few discussions here in the forum over the past 6 months about problems that arise from low voltage on the Vehicle Power Supply Battery (the left side battery). As most of you know by now, if the voltage level drops below a certain level on this battery, the Phaeton will sometimes generate fault messages on the Y24 display (the screen between the speedometer and the tachometer), such as "Suspension Fault - Workshop" or "Running Gear Fault" or even "Brake Fault". Truth is, there is nothing wrong with any of these components - these messages are only being generated because of low voltage being supplied to the controllers for the different items such as suspension or ABS. Easy enough for us to say this in the forum, but that's small comfort to a new Phaeton owner when they are confronted with these stern messages during their first month of ownership.
This raises the question "Why is the battery voltage low in the first place?" As we have learned, there can be quite a few causes for low voltage on the Vehicle Power Supply Battery. In approximate order of probability, the causes are as follows:
1) New Phaeton owner is sitting in his or her Phaeton in the garage, listening to the awesome sound system, and reading through the owner manual, trying to figure out how the car works. Engine is off. After about an hour, the battery runs down.
2) Phaeton is at the VW dealer getting some kind of service done (maybe an oil change), and the Phaeton technician either does not hook up a battery maintaining system to the car, or, hooks it up to the terminals under the hood, instead of hooking it up to the Vehicle Power Supply Battery.
3) The Vehicle Power Supply Battery is 'worn out', because the Phaeton was sitting in the showroom as a demonstrator for 3 months - without a battery maintainer hooked up to the Vehicle Power Supply Battery - and the battery went flat so many times that now it is incapable of holding a full charge.
4) Something drains current from the Vehicle Power Supply Battery when the Phaeton is parked for a week, unused, in the garage. This might be the little portable fridge or DVD player an owner forgot to unplug from the 12 volt outlet, or, it might be some rare, strange fault of a system in the car that continues to draw power when it should not draw power.
5) For some reason, the Phaeton is not fully charging the (healthy) Vehicle Power Supply Battery when it is being driven.
I encountered the problem of false warning messages on my Phaeton several months ago. I took the car to my dealer, who checked the car out very carefully. He ruled out number 3 (above), because my dealer had installed a new left side battery as part of the PDI process - my Phaeton had been in the showroom for 6 months before I bought it. I knew the problem was not caused by item 1, and the Phaeton technician knew it was not caused by item 2. I ruled out problems that I might have caused related to item 4. We didn't think it was probable that I had a rare, strange problem of some other system. The guided fault finding system that the technicians use (part of the VAS 5052 scan tool) suggested that the generator be replaced. The tech at my dealership thought that was not a good idea, and disregarded that suggestion. So, that left item 5 as the only 'probable cause' of my low battery charge condition.
Around the same time, there were some posts made by other owners who were having the same problem. Joe (jmdpjd1) posted about his problems, and the experience he had - his dealer replaced both of the batteries. That post is here: Two bad batteries. Rodger (phaeton Also) posted about his problems in this thread Report on first 3000 mile trip. As you can see if you read his thread, he had a whole slew of problems, and his Phaeton technician replaced his J367 Battery Monitoring Controller with a new one at part number suffix C (software revision 2700) status.
Since my problems were happening at the same time as Joe and Rodger's, the Phaeton tech at my dealer and I decided we would wait a month or so, and see how things worked out for Joe and Rodger. In the meantime, Robert (iluvmcr) made a post about his electrical problems here: My Phaeton's electrical problems long gone, and that thread evolved into an interesting discussion of Principles of Troubleshooting.
Well - after six weeks passed, Rodger reported back that his Phaeton was trouble-free after having had the Battery Management Controller replaced. This whole issue of battery discharge also came up for discussion at the German Phaeton owner get-together, but the German owners reported that it was uncommon, and in any case, they never had to go back to their dealership more than once to get it fixed. I discussed this with the Phaeton tech at my dealer, and we decided that it would make sense to replace that same controller on my car. During the 6 week time period, I had been very careful to not do anything that would discharge the Vehicle Power Supply Battery, but despite that, my battery showed that it only held 80% of a full charge. Since we knew there was nothing wrong with the battery itself, the logical thing to do was to replace the Battery Management Controller.
I was allowed to watch the process, and I took some pictures for the forum. I won't really know for sure if this action - replacing the controller - was the right decision until about a month from now. I know that the 'baseline' charge level for my battery was about 80% (414 amps out of 480 total) before replacing the controller, and this was after 6 weeks of being very careful to not discharge the battery in any way. In about a month's time, I will take my Phaeton back to my dealer, and we will check the battery charge level again. If it is significantly higher than the baseline, then that should prove that we made the correct choice.
I'm not suggesting that replacing this controller is the magic answer for any electrical problem on a Phaeton. But, it does seem to have solved the problem for Rodger, and in a month or so, when I take the car back to have the battery charge level checked, we'll find out if my Phaeton is doing a better job of keeping the Vehicle Power Supply Battery fully charged as a result of replacing this controller.
Just a postscript: On the way home from my dealer, I stopped by another Toronto VW dealer just down the road, to say Hello to a forum member who works there as a salesperson. He showed me a Phaeton sitting on their back lot that VW had just bought back from a customer (they replaced it with a 2005). It was waiting for VW to pick it up and send it out for auction. I asked him what the problems were. It seems that Phaeton had all sorts of electrical problems - fault messages about suspension, brake faults, running gear faults, etc. - and it had been in for service numerous times, but the messages kept coming back. It's unfortunate that this buy-back happened, because I think we might have figured out how to identify, and possibly solve the cause of these problems. My guess is that a battery management controller replacement is less expensive than a buyback.
Checking the health of the battery using the special VW Battery Checking Tool
It is not necessary to take the battery out of the Phaeton to do this. It was just easiest to take pictures this way.
The printout from the Battery Checking Tool
Although my battery voltage was good (11.93 volts), the battery was not fully charged - only 414 amps out of a possible 480. The tool recommended that the battery be recharged. This was, we think, the key diagnostic point in figuring out the whole problem. If the battery was not fully charged after I had just finished driving the Phaeton for 100 miles on a summer day - then, the Phaeton was not sending enough 'recharge' back to that battery.
Part way through the disassembly process
The relay panel has been removed and set to one side, and the bolt holding the battery in place is being loosened.
Location of the J367 Controller
The old and new controllers