pcjn

Hi,

I've previously posted about a serious battery drain I had on my 2004 Cayenne.

I eventually seemed to fix it but disconnecting the 'radio'. After testing it, the drain was now acceptable (using a multimeter) and it worked fine for 2 months or so.

Now though, it's gone again. I have to use a Hummer battery starter most of the time (which I believe isn't good for the battery?).

I don't understand it. This car has been stripped and no one could find the fault (many mechanics and porsche themselves). Eventually I read about disconnecting the radio (even though the fuse was already pulled) as someone else had that issue and it worked. For a couple of months...

I've held off asking for help because I wasn't sure what I could add to give you a clue, but I've noticed something. Sometimes it does start, but it can take a turn or three to work. The first time it may just turn over once, weakly, and then on the second or third attempt, if I hold the key to the right, it finally kicks in. It seems dead, but it isn't.

But other times when I do the same thing, holding the key to the right causes the power to completely reset in the car.

Does this provide any clue as to what the problem could be?

Thanks

deilenberger

Sounds like an old tired starter combined with a bad battery. If the battery has been discharged frequently so that it needs to be jumpstarted - the battery is now trash. Get a new one. If the new one doesn't fix things up - then consider that the starter is 14 years old and might be getting rather tired. If the above don't fix the apparent discharging (which could just be the bad battery self-discharging) - then you need to do a current draw test when the vehicle has gone into sleep mode. If that sounds like Greek to you - perhaps professional help is needed.

pcjn

Thanks deilenberger. Taking your reply backwards I spent thousands on professional help and no one could find the original cause of the drain. It took me a few hours of research and a few hours testing (with door switches jammed closed, in sleep mode etc) and - even though from my research I thought it may be the headunit - I did a full test on everything just in case it was more than one problem. But sure enough, once I disconnected the head unit, the drain stopped.

I was just confused as to why t would suddenly start again after 2 months.

I have been wondering about changing the battery - having gone through a lot of them in recent years - I'm reluctant to do that and end up jump-starting it again. But I guess you are right. The next step is to get another new battery and see how it goes. If it drains just once, I need to quickly move to look at the next possibilities - the starter and alternator.

Thanks

Petza914

I would check all the grounds for the battery and for the starter. That starting symptom you've added could be a bad ground for the major amp draw during the starting process. A bad starter could draw so much amperage it looks like the same thing. Is there any record of a coolant line repair in the service history? If the starter gets doused with coolant from a bad leak, it can take anywhere from 6 months to 2 years, but it will fail as a result of that event.

deilenberger

Just wondering - as when odd electrical things happen in a Cayenne - it's most often bad splices in the wiring bundles running under the carpeting in the driver/passenger footwells.. has this been checked?

pcjn

I've had the car longer than that, bought it from the original owner about 6 years ago?

I will do those checks though. Thanks

pcjn

Yes. The car has basically been stripped. One of the problems (although not THE problem) was some burnt out aftermarket wiring for tvs that the previous owner put in the backseat headrests. The wiring was taken out, and anything damaged replaced.

That still didn't fix the main parasitic drain. That only stopped when I disconnected the headunit. But as I said, 2 months later and having problems again.

I really think they must be unrelated problems though, so I am leaning towards either the starter or maybe just the battery being buggered after too many jumps before.

PTEC

Since its a 2004, your cayenne doesn't have dual batteries does it?

pcjn

Not that I can find

In the boot (trunk) there is the bose subwoofer so from what I can gather that means I don't.

This morning before I set off I checked the voltage of the battery with a multimeter and it was around 9.7v so obviously I needed to jumpstart it (it's one of those Hummer jump starters, like this - )

When the engine was running the voltage read at 13.98 or so (I didn't write it down, but about that).

I drove a few miles and parked. When I set off again in a couple of minutes, before starting, it read a 12.47v.

It started without the jump start (but some days, the exact same trip, it needs another jump).

When I got back I parked and checked and it was still 12.47v.

I'll go check it in a few hours (waiting in for a parcel at the moment though...).

But does this provide any further clues? Obviously there is a drain still (I drove it last night - about 30 miles?) so it should have been ok when I parked about 9pm but at 10am it was down to 9.7v.

Does this rule out the starter as the main cause of the problem? (Obviously there could be a problem with the starter too but would the starter cause the drain ?)

I'll have to do a new test to check everything, it's just frustrating as I've done this before only recently and removing the head unit fixed it!

Thanks

deilenberger

Still sounds exactly like a failed battery. 9.7V is a dead battery. It's not coming back. It's kaput. Dead. Nailed to the perch. Gone to meet its maker. Not here.



Sounds like your alternator is working just fine, but having a tough time trying to charge a dead battery. The 12.47V was what's called a "surface charge" - where it has a reasonable voltage, but no capacity for load (ie - current) - and if you had turned on the rear-defroster, it would drop down fast enough you could watch it.. 30 miles is not far enough to recharge a dead battery. And driving it at night means headlights were on - so current available to actually charge anything was minimal. Voltage from the alternator might look OK - but most of it is going to the headlights and other normal current consumers on the P!G.

Any battery that has repeatedly experienced 10V or below is basically just a lump of useless lead.

Petza914

+1

The old battery I pulled out of my Cayenne would show fully charged on the bench top charger with 2 different chargers - an Optima and a Schumacher, but when in the car wouldn't turn it over, not even once and the hatch would get stuck about 1/3 way up. With a new battery everything works perfectly.

Marv

So, your battery is bad—really bad.

Your car's charging system is good.

Go get a new battery. I've had good luck with Interstate Batteries in both my GT3 and Cayenne.

Petza914

I put a Napa Legend Premium AGM in my Cayenne. Proper H9 size and 18 or 24 month full replacement warranty, prorated after that.

PTEC

I want to say you could still have the dual battery setup even with the sub in the back. If you have your build sheet check for option "J2C" as that is the option for dual batteries. If you can confirm your dont have the dual battery setup it really does just sound like your battery is bad. Also the voltage dropping could just be the battery being toast, it doesn't necessarily have to have a draw. The first step of any electrical diagnosis should be 100% sure you have a good battery, if the battery isn't good you're wasting your time looking anywhere else. I would definitely start with a new battery see what happens and if the engine still labors to start then the starter is probably worn out and needs to be replaced. As deilenberger has mentioned a worn out starter will kill batteries over time in a otherwise perfectly healthy electrical system.

pcjn

Thanks all, I'll get a new battery then!

And thanks PTEC, I'll have to check that, I thought if you had a sub there was no battery so never looked any further, but I will now.