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Papagut

Critical electrical system fault(s)

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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

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I agree its most likely a control unit that has gone bad or a battery on low volts

The power from the battery goes thru the computer if the computer senses low battery capacity is shuts down non essential services and goes into "get to a dealer" mode.

Before wasting to much time I would replace the battery, on an 04 it must be close to end of life so will not be wasted and it will be a whole lot cheaper than a replacement module.

What services are off ?

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

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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

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Have you inspected the gound point and power supplies located under the left front seat near the battery? There are several fuses and a reset breaker located there.

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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

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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.

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Are you sure you are not confusing a ground cable with a power cable? There is a power junction block that has several fuses and a breaker type device under the seat. These are complicated vehicles and it might be best to take it to someone familiar with the system on the Cayenne.

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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.

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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

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The only way to really test a battery is to take it out of the system (out of the car) and have it load tested at shop that has load testing equipment. AND each cell should be tested for specific gravity readings within an acceptable range.

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This faults are the most common when you have lack of power in the battery.

The questions for you is, do you only drive short distances? Do you often let your car rest in a week or two?

If you have answered yes of one of these two, I should replace the battery :)

One more thing, do you have two batterys in your car? The dealer mabye changed one of those ?

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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?

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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?

When you are driving short distances, the generator cant refill the power that are needed when the car starts. The starter takes a lot of power. Thats why I asked that question. If you are going at longer trips some times, then the battery will load up.

BUT... If the battery goes almost empty a couple of times, it will be weaker.

The generator are often in full function or broken in these cars. Nothing in between. Ofcourse some cars will have a half broken generator but I havent seen it yet. (worked with porsches for more than 3 years)

If you can, try to put a charger over night and see if the problem are gone next time you start the car. If its gone, then its defenetly the battery.

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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.

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Well, I was very hopeful... I had the existing battery tested, and it did fail, so I thought that I may have found the root of my problems. However, with a new battery in place, and after running the car for a while, my electrical issues remain.

Any thoughts?

Mark

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Well, I was very hopeful... I had the existing battery tested, and it did fail, so I thought that I may have found the root of my problems. However, with a new battery in place, and after running the car for a while, my electrical issues remain.

Any thoughts?

Mark

Have you tried an OEM battery? They are about $200 each. (95AH, 110AH etc.)

Edited by TopGun2000
  • Upvote 1

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here you go:

Cayenne V8

Electric system

Electric system

Radio interference suppression ECE-R 10 and 95 / 54 / EC

Nominal voltage

V 12

Battery capacity

Ah/A 90

Starter

W 1900

Rated generator output

W 2660

Table:

Battery capacity: 70 Ah 95 Ah 110 Ah

Cold test current 340 A 450 A 520 A

Edited by TopGun2000

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Thank-you,

At this point, I am again ruling the battery out as the source of my woes. If anyone has any ideas on why I am experiencing these electrical issues, in particular something like the location of the control unit that deals with the mentioned functions so I can test the power to it - or a likely wiring harness or connection that may have failed, I would greatly appreciate it.

Otherwise I feel I will have no choice but to take it in and have it looked over at a dealer.

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There was a TSB for a faulty battery cable from the alternator to battery that caused odd charging system issues. Have a dealer check your VIN number to see if your vehicle has been done.

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Why so complicated?

If you cant change the gearstick. Some signal is missing to the control unit. You have ABS and PSM fault aswell. You need signal from the brake switch to release the gearstick. If you are missing signal from that switch you cant move it. The ABS and PSM control unit needs that signal aswell, otherwise this alerts will come up.

Simple test, Do the brakelights go on when you press the brake pedal?

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wvicary - checked with dealer, and it is up to date, that is, all issues on this car have been serviced.

deikoo - I think you are heading in a different direction, but the brake lights work fine.

Can either of you tell me the physical location of that control unit so I can check the connection and the power flowing to it? I feel I am going to find a damaged pin, frayed or damaged wire, or a short of some kind that is causing this problem.

Mark

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Solved!

I started with the fuse box on the right dash, as I mentioned, the bottom two rows of fuses were getting no power. I disassembled the dash and fuse box and identified the power lined feeding these rows, there were three power lines. Following them back into the thick harness that runs from the fuse box then under the carpet passenger side, I found that all three are actually spliced together to form a single power line within the wrapped harness.

Following this single power line, it ran back up and into the upper dash, along to the driver side of the car, down and under the carpet to a relay (the only one) mounted right beside the battery. At that point I tested the power and ground going into the relay, and also disassembled the relay itself and tested it. Power and ground were fine, but the relay was not tripping and providing power to the systems upon ignition.

So next step was to test the power used to engage the solenoid and complete the connection. Power was fine, ground was not. I followed this small ground back up the harness and at a position roughly where your left foot rests, there was a series of spliced connections for a number of wires (again, within the wrapped harness). That was exactly where I located that this wire was spliced, and had corroded and came apart. I cleaned the wired, soldered and wrapped, and all systems are perfect.

In the same location, there were a number of spliced connections, I inspected all of them and found another getting close to failure, so it was repaired in the same way. Then I resealed everything, and have no problems.

To hopefully assist anyone with a similar electrical issue, pictures are attached: battery shows where the relay is that powers the systems (top right, relay removed, purple), harness shows the stripped wiring under the carpet, broken shows the connection as I found it.

Ultimately, I believe it was moisture and salt that corroded the connection, although it looked poorly done in the first place. Thanks to everyone for your help, and please e-mail me if you have any questions of comments.

Mark

post-51826-1270562281_thumb.jpg

post-51826-127056229082_thumb.jpg

post-51826-127056230003_thumb.jpg

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Result... glad you got it sorted and thanks for posting your findings.

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I have the same problem as of right now(Break proportioning & abs light and brake flashing light is on the dash)looks like Xmas tree in my dash😒👎, I lifted the carpet in the driver side and check the wires everything seems about right, there is absolutely no corrosion, or spliced wires, on the other hand the other day I was washing my truck and went to open my trunk to dry it, and I seen water creeped in the left rear driver side panel so I'm gonna take off that panel and check the rain gutters to make sure there Not clogged as this may be a culprit too my problem😔 any suggestions or help will be greatly appreciated😁👍

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I had similar issues on startup and fixed them by replacing the terminal 15 relay that sits on top of the battery underneath the drivers seat. $18.

It's a standard looking relay box and is the only one under there. Access either by unbolting the front seat as described in the owners manual as if replacing the battery. Or with a little less trouble by sliding the seat all the way forward and up. That should get you close enough to access the relay from the left rear seat footwell.

I should add that I spent a lot of time going through both the front footwell floor areas looking for water damage. I found none.

Edited by jagman1

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