Simonm1

Hi again guys I've got another problem with my 964 heater control. After all the help I got with my central locking problem I think im in the right place for gurus. What's happening with my car is that the battery keeps draining pretty quickly I've narrowed it down the being in the heater control some where. It's pulling about 1.5 amps with every thing turned off. Has any one had these issues or can any one shed any light on this for me thanks again

Rocket Rob

I had this problem and fixed it. Let me see if I can find the thread.

Edit - here they are.
https://rennlist.com/forums/964-foru...ery-drain.html
https://rennlist.com/forums/964-foru...king-amps.html

Simonm1

There is some really good guides in there I've removed the ccu from the car and have seen tores page a little while back. Is it common for the transistor to give up and how do I test if it is the transistor. I've picked up some bc337's and wil give it a go but would like to test it before whipping it out

JasonAndreas

There is no way to test the transistor in-circuit BUT if the fan at the back of the CCU does not turn off, then BC337 is your problem. The other telltale will be a current draw of ~500mA. Your 1.5A is likely to be something else!

Jacke2c

It sounds like a frunk light or rear deck lid light… That is what I measured them at (1.5 amps) when I was trouble shooting my car. Did you check the interior lights to insure they come on when you leave the car and turn off when you close the door. The ECU will remain "hot" until it knows you have exited the car. These switches can easily work intermittently and if you turn off your engine and get out of the car and the light doesn't come on and off as the door is opened and closed you can still operate the accessories. IF the switch is working as it should, you should be able to sit in the car after you have switched the engine off and still operate the windows, etc… But after you open the door and the interior light comes on, it resets the computer to off and after closing the door (still sitting inside), you should not be able to operate the accessories.

Simonm1

I've put the amp meter in series with the battery and with the ccu fuse pulled my amp drain disappears have unplugged the ccu and car seems fine with it removed I didn't check to see was the little fan running before removing it tho ill plug it back in and see what happens when I can get back to it

ToreB

As mentioned above, the CCU can develop a fault where it does not shut down at ignition off. Normal current draw in this situation will be about 0,4-0,5A. The CCU fan will be running, but as the fan wears over time it can be stationary due to this anyway.
Removing fuse 1 (or disconneting the battery) will reset the CCU, and it will remain shut down until ignition is turned on again.
Be sure to measure any current draw with both doors shut and engine/luggage compartment closed to avoid other active circuits. Depress the luggage compartment lock with switch in a 993 (and late 964?) to be able to work there, earlier 964 models has the trunk lid light switch mounted on the right side of the luggage compartment.
Disconnecting an amperemeter connected in series with the battery will also reset the CCU, so leave it connected and turn on and off the ignition fast to see if the CCU shuts down normally. (within 5 seconds) Leaving the ignition on for more than a few seconds will make the CCU to stay on for up to 20 minutes.
Cheers,
Tore

Simonm1

Ok as soon as I get back to the car I will recheck as its been a little while since I got my readings do will double check every also I removed the bulbs from trunk light to eliminate that. All seems well with the ccu removed but will recheck the amps draining