freedman

This may well explain my newly developd battery drain

Deleted the sunroof, and along wth it the interior lights

Now have a drain and the odd flashing door locks

Anyone got any idea how I need to deal with the redundant writing to correct?

Jeff777

I am having a problem with battery drain on my 92 C2 which started with a residual drain of .47 amp. This draw was traced back to fuse 1. The ECU was pulled and a faulty transistor replaced (Thanks Tore B!). The draw was reduced to .05 amps, about normal I think with a aftermarket radio. A new battery was just installed. The alternator was pulled and tested ok but had the voltage regulator replaced anyway. The drain is still .05 amps and the battery is STILL discharging over a couple of days. How can this be? Anybody with any ideas would be greatly appreciated!

ToreB

I cannot see how a 75Ah battery can discharge in a couple of days with a current draw of 50mA. it would need to be 5A to do so. The battery is most probably defective, or unsufficiently charged.

See here for a detailed procedure on how to measure the current draw in the 964/993.

Cheers,
Tore

dlpalumbo

My car will discharge it's battery within 2 weeks. I have measured drain at 17 ma. Doesn't add up. But, I have noticed that my oil/AC fans will come on occasionally and run even when car is off. My thinking is that a minor drop in battery voltage is leading to circuitry confusion, especially in CCU. A rebuilt CCU at $1000 is a bit much for a WAG at problem, so I keep car on trickle charger.

ToreB

I have never seen evidence that a voltage drop from a dying battery would fire the cooling fans in the car. The CCU shut off within 20 minutes after ignition off, and it impossible that the fans will start in this condition. This is unless there's an external reason such as a failing fan motor relay.

A malfunctioning rear duct temp sensor could cause the CCU to run the rear fan when the unit is on, and this might in effect empty the battery. The fan motors are drawing around 20A each. The CCU will shut down within 20 minutes anyway, if the battery holds that long.
However, this is mostly caused by a weared-out fan relay, causing it to stick on.

Based on this, I can't see how a CCU job at any price would fix the problem.

Cheers,
Tore

dlpalumbo

Thanks for insight Tore. I'll put fan relays on my list. Haven't seen evidence of door sensor failing, so I am groping for an explanation for 2 week limit. Shop complains for having to charge car when its in for weeks...

Jeff777

Thanks Tore B. I've gone through the procedure again. Battery fully charged. The drain seems to be steady at 50-60 milliamps although at one point it got up to .3 amps. Pulling the fuse 1 got it down to .02 so there may be still a problem there with the CCU. I couldn't duplicate that and the draw seems to be back down to .06 amps. As I mentioned I had the transistor replaced on the CCU. I will get the new battery checked and probably wait until I receive your T OBD kit for further evaluation. Door switches seem ok. If there was a faulty fan resistor would this show up as parasitic drain?

ECU Doctors

Hey Guys, we just made this timely video for Rennlist.

We know that battery drain has been an issue with these Porsche 911 964 996 CCUs for years and so when we designed our upgrades climate control units this was one of the flaws that we wanted to fix first.

Here's a quick demo:

ToreB

A working CCU will not drain the battery.
The unit is designed to stay on for several minutes after ignition off to maintain a reliable measurement of the cabin temperature on short stops.
In addition, the CCU measures engine temperature and will run the rear fan in cooling mode if needed during this period to reduce engine temperature at standstill.

I see no reason to upgrade or change the unit to avoid this.

Cheers,
Tore

Lorenfb

Totally agree!!!

Jeff777

Guys,

Thanks for the info. My battery drain continues on my 1992 C2. Here's what I've done so far:


1. Alternator pulled and checked and voltage regulator replaced as precaution.
2. Transistor replaced on CCU(draw was around .47 amps.) Transistor was defective.
3. Battery replaced.

For awhile the drain was .06 amps but the problem returned. Here’s what I have today following your procedure:

First Battery drain .36 amps
Pull fuse 1. .02 amps
Put fuse 1 back in. .065amps....why not back to .36?

Ignition On(1sec) .7 amps
Off. .30 amps

Did another parasitic drain test and got around .06, not too bad. This would not drain the battery in a few days. But when I checked 30 minutes later it was back up to .37. How can this be? Somehow I think the CCU is turning something back on. Door switches check out and all the drain seems to disappear when pulling fuse 1.

I have used the T OBD and ran the test outputs on the CCU, all seem ok. Can't get the trouble codes sorted out yet(another problem). I think the next thing is to pull the CCU unit out and see if the battery still drains.

Any thoughts?

Thanks

ToreB

I have previously not seen any cases of the CCU turning itself on if shutdown. It needs +12V on Terminal 15 input to power up. However, there's a first time for everything. There might also be a fault in the ignition switch or elsewhere that activates the Terminal 15 network briefly, causing the CCU to wake up again.

You write that you checked the current drain after 30 minutes. Did you leave the amperemeter and battery connected during this time, or did you briefly disconnect the car battery to do this measurement?
Upon connection of the the battery, many units in the car will wake up, but shut down after some time.

I have made a DIY page for current measurements in the 964/993. See here for details.
Cheers,
Tore

Jeff777

Hi Tore

When i checked the current draw after 30 minutes I did reconnect the battery. It initially was around .63 and then dropped to .37 after a few seconds. Yesterday I fully charged the battery 12.9 volts and the current draw was .06 amps. Today, after 16 hours it is down to 12.3 volts.

It is a new battery but I will take it out and get it checked. If ok, I think I will remove the CCU and see what happens to current draw on the battery over a few days. If it still goes flat I guess I can eliminate the CCU as the culprit. Do you agree?

Cheers
Jeff

Jeff777

I removed and disconnected the CCU. The current drain dropped from .36 amps to .02amps. The battery is normal so I guess the culprit is the CCU. Time for a rebuild? Anybody have any other ideas?

Railmaster.

Was the internal fan inside the CCU shuting down like 10-15 minutes after You turn the engine off? Mine didn't and I had to DIY change (soldering iron required) a tiny component for like five cents in there! Now it runs perfect and does not drain my battery any more!