Hi guys. I bought a 2004 Porsche Cayenne turbo. Two days after buying it I drove a mile from the house, turned it off and it wouldn’t start. It was cranking over but nothing. The radio sometimes wouldn’t come on. I finally got it started and drove it home. It died a couple times on the way but started again. After it got home I got a new battery for it. The error went off PSM and it started running. All was well for 1 drive. I took it to the auto parts store and checked for errors and there were none. Before the new battery the error was P2403 Evaporative Emissions System Leak Detection Pump Sense Circuit/Open.
The next morning I go out to start it and it won’t even try to crank. All electronics come on but it says press brake pedal, even though it is being pressed. The fuses seem good and the starter fuse relay seems good. I checked the 2nd battery and it had some corrosion so it was cleaned and a giant fuse was replaced. (Sorry I don’t know all of the technical terms.) If I turn it over sometimes it will turn on the display and sometimes it is blank. The engine fans will come on without it being started and even stay on after the key is taken out. (The battery is being disconnected while we are not working on it for this reason.). The wires under the dash look like a hot mess to me. There is a brown and yellow wire that seem to just be cut.




When the key is turned on sometimes now I will hear a click from a fuse under the seat and all electronics will turn off. When she ran it was great. With all the things going wrong I can only assume this is electrical.
I have no idea where to go from here. The mechanics here can’t look for a couple weeks and only 1 will touch this thing.

 

First look to see if there is anything aftermarket installed. If there is remove it and all the wiring for it. You can always re install properly after you get it working properly in stock configuration.

 

Do you know if that black box is supposed to be there or if that is something aftermarket? I don’t really know what is supposed to be there and what is not. There is a box about the length of my hand under there. Do you know if that is supposed to be there?

 

Follow the wires and see where they go.

 

I would say no to that black box. I just looked under my dash and don't see anything like it. Going out to take a few pics now. Have a look in the front grill. That black box might be for laser detection???

 

Thank you, I will check when I get home. I don’t think it is supposed to be there because that bundle of wires is a hot mess! What is laser detection? Does that come on the car? Thanks for your help!

 

A laser detector is like a radar detector, but for laser. It is supposed to detect and jam the laser signal. Does not come stock. You will find little square boxes in the grill.

 

Here is what under my 2006 turbo s looks like.

 

More

 

I am definitely not a wiring guy but I had a laser jammer in mine that was creating a parasitic draw. Totally removed the thing and fixed that. Good luck and hope you find the issue.

 

Thank you for the pictures. I wish mine looked like that. I will check for the laser. The guy did 4,000 miles in 2 months so it is possible he had one for that much traveling.

 

I would take a different approach and not focus on any wires right now. At least don't make things worse...
Unfortunately, in my experience, when you have the two batteries, you have to treat them as one in that you can't ignore the rear one. -It sucks down (and wastes as internal heat) any juice that the main battery needs to recharge.
Try disconnecting the rear battery and go for a long drive to see if that solves the issue. Or replace the second battery. If you check the date code on it, it's probably ancient.
My 2 cents.

Edit: I took another look at your wires and yeah, fix that. But still keep in mind my advice as you troubleshoot. Good luck and welcome!

 

My appointment is finally here to have the shop look at it. I had to tow it over last night. It wouldn’t even stay on enough to get it into neutral. We jumped the back battery and got more response then we have in a week. When I talked to them before taking it over they did say you typically want to replace both batteries at the same time. He also said you want to program those batteries to the car using the Porsche tool. Hopeful that this will fix the issues. I will update y’all when they get done and get it figured out. Thank you for all the help. This was the best!

 

I'm glad your optimistic and I hope you get your Porsche running, but at the risk of seeding mistrust, there's no programming or coding involved in replacing your battery.
Maybe your mechanic was speaking of something else.
Best,
Steve

 

What they said is that the computer is fried. Someone had been in messing with it and obviously covered this stuff up to sell it. He said there is nothing he can do. I would have to contact a Porsche dealer and see if they can put in and program in a new computer.