Papagut

Hi there,

I am having some electrical issues with my car, and I am suspecting the battery that was replaced about 9 months ago. I had a shop replace my starter and they told me that the car had "the wrong battery in it" - and that they replaced it with the correct one. About 4 months later some electrical issues start cropping up. It starts perfectly, but some important functions fail. The battery that they put in is a:

Interstate Mega Tron Plus, MTP-93, 850 CCA 1000 CA

Not the battery recommended for my truck on the Interstate site. Can someone let me know if this is an appropriate battery for my car - an 04 Cayenne Turbo? I do not mind using a non-Porsche battery at all, but just want to make sure it is the proper rating and if it is perhaps the source of my woes.

Thanks,

Mark

After looking, the battery is an Interstate Mega Tron Plus, MTP-93, 850 CCA 1000 CA. When checking it against the Interstate site - they recommend another model of battery, but do not provide good details on the rating of this particular battery, and it is also quite difficult to find the details of the OEM Porsche battery too, so I can compare the two.

Let me know if this looks like it is the obvious root of my problems, but my next step will be to have it tested / charged, and at the same time I will post a new topic on just the proper battery type for this car.

Thanks,

You know, I have been kind of assuming the battery is fine as it was replaced less than a year ago, but now I am remembering that the shop that changed it told me they had found that the one they pulled out "was the wrong battery". Perhaps they were mistaken, and this new battery is causing problems.

In terms of trips, we do use it frequently for shorter distances - let's say 10 KM per trip daily - but not little trips to the corner and back. But having said that, they are mixed with semi-frequent longer trips of 300-400 KM. I am going to look into the battery and will post back the results.

Is it also possible that the alternator is failing to charge it properly? or is that more of an item that will either work or fail - not degrade?

Okay, no need to post picture. I folded the seat back and inspected all the wires / fuses again. All are supplying power, none are burnt out. The breaker is not tripped either. In an earlier post, someone mentioned that it could be low volts or a faulty control unit, which leads me to two questions:

What is the proper volt rating and what should the battery be outputting - so I can test it?

What is the location of the control unit that handles brake proportioning and air suspension - so I can check the connections there too?

Thanks, Mark

I will fold back the seat and have a closer look, but they are both black, with the power lines all coming out of the same area in red. I will take a picture and post it tomorrow.

Okay, perhaps some progress:

Under the drivers seat there are two large ground cables leading to the battery compartment. One attaches with a bolt to the floor a few inches from the compartment - and was my first candidate to check as there was some salt and rust around that area. However, when uninstalled and checked, this cable forms a clean connection. The second large ground comes out from the area just beside the battery, and snakes away from there (not affixed to the frame of the car anywhere near the battery). This ground is anchored to the plate that is just beside the separate battery compartment - the same area where there is also some fuses and a relay, and where there are large fuses for the red power lines too. If I test the two ground lines from a power source with the car running, current flows through the ground anchored to the body of the car, but not through the one anchored to the plate.

Am I onto something? Should that second ground also make an active ground connection with the car running, or is it related to something that only forms a connection briefly - like the starter?

Thanks, and let me know what you think.

I am going to take another look - but the short answer is yes. The fuses are all fine, and the ground point looked okay by a quick visual inspection, but I will take it off and clean it to be sure. However, I did do the following: removed the fuses from the area of the box I have been describing, then tested the ground connection there by running power from another connection through it. It appeared to be fine, which is the point when I ruled out the ground connection as the failure (which was what I suspected first).

Mark

Thanks,

On the battery note, it was replaced new when I purchased the car - about 12 months ago, so I suspect that low volts is not the issue. I suppose it could be, but it is not laboring at start, and no other electrical systems are offline. Then as for the module, I also suspect that it is functional as when I provide power to this part of the fuse box, all of the functions come back up.

Since providing power at the fusebox does the trick, my first expectation was to find a defective relay (all of the systems in question only get power at ignition). While troubleshooting this I found a set of 6 relays under the steering column. Two of the 6 are small and black and marked with a "404" on the top. If I remove one of these, it replicates the warnings (the systems in question go offline). However, I can hear them click at startup, and swapped each for the other with no change - so I also suspect that the relays are fine.

The three critical systems that are locking the car in park are "disk brake proportioning", "PSM", and "air suspension" - but like I mentioned, it takes out all functions in the bottom two rows of the right side fusebox.

What I am expecting to find is a broken or loose connection somewhere between the relay and the module. On that note, I have checked all the connectors to the modules I know of looking for bent pins or corrosion - they all seem clean and fine.

Let me know what you think. If you can ID the module in question, maybe I can verify if it is receiving power.

Mark

Hi there,

First of all I am brand new to these forums, and this is my first post, so please feel free to let me know if you need more detail. I have worked extensively on the mechanical systems in my car - an 04 Cayenne Turbo, but am confounded by an electrical system fault. Here is everything I know:

- when starting the car, I get "brake proportioning" and "air suspension" red alerts on the dash, and the car cannot be shifted into drive (unless you release the shifter lock manually).

- right side fusebox, the bottom two rows are all non-functional - that is, all systems that have fuses located there are offline. Everything else is fine.

- these fuses all use a common ground connection which looks like a bar running across the lower connection of each row from the back of the fusebox. This ground connection has been tested and I believe it is fine, but I could be wrong.

- if I provide power to any or all of the individual fuses, that particular function comes back up.

- all of the fuses have been checked of course.

I have done a lot more testing of the circuits, looking for any signs of where the break is occurring, so I have documented quite a bit more than just this. So, let me know if I can provide more info.

I suspect that there is either a break in the power that is common to these systems further upstream, such as power going to a module that controls all these functions, or a break to the ground circuit for these systems (and I am not testing it properly).

Your help would be very much appreciated.

Mark