jjbunn

I've been reading a lot of threads about excessive battery drain in our cars, and what people have done to try to diagnose the cause.

The reason I'm interested is that I've always found that the battery will drain if I leave the car for more than about a week without firing her up. After several flat battery episodes I decided enough was enough.

So I got a new battery, but before connecting it up, I checked what the current draw will be by placing an ammeter in series with the +ve terminal of the battery and the +ve battery cable. I removed the bulb in the under-hood light.

After connecting the battery, the current goes to around 270mA, and then after a few seconds drops to, and remains at, 120mA.

This seems too high to me, by about a factor of six

Thus I started pulling fuses in the front box, and none of them made any difference. Ditto for all the relays in the front box. I haven't tackled the fuse box in the engine compartment yet.

I don't think this is an alternator diode issue because I'm testing the draw to the main/thick +ve battery cable (not the smaller red cables).

Any advice or words of wisdom would be much appreciated.

Thanks!
Julian

deep_uv

Julian, exactly my experience. 120mA no matter what fuse I pull. I replaced my alternator a while back (it suddenly went bad) and still have the same 120mA draw afterward. I quit worrying about it. My battery will last 3-4 weeks if I don't run the car. I rarely go that long without driving it.

jjbunn

Thanks, Steve: that's good to know.

It would be nice to know what is drawing that current, though, and why it isn't on a fused circuit.

DWS964

I have a similar problem. Same diagnostics. Alternator just replaced. One remaining circuit that I suspect - the alarm system is fused locally at the module under the seat. And my car has an aftermarket alarm installed in addition to the stock alarm. I am betting $0.25 that the problem is in there somewhere.

elbeee964

Wish I had a reason and corrective action to throw at this thread.
But I don't.

Instead, I wussied out, solution-wise, & bought one of those Porsche battery maintainers and leave the cord sitting alongside the door on the garage floor whenever I'm ready to leave the garage. First and last step for any drive deals w/ taking it out/plugging it into the lighter socket.

Gives me that Jay Leno moment when I get into my collector car in my super exclusive car collection garage.
Or I take the corolla.

Rocket Rob

If you have pulled all of the fuses and the current draw remains, I would start looking for hard-wired items. Do you have an aftermarket stereo or alarm? I would look for any wires that look "non-factory" and start tracing them.

In my case, I had an excessive current draw myself (400ma) earlier this year. After 3 weekends of troubleshooting and scouring the wiring diagrams, I found it. I was able to isolate it to Fuse #1 and then isolated it to the CCU.

Good luck on the repair

911URGE

I got this from Porsche TSB 9402 Battery - Discharged Unit Diagnosis

Date: March 29, 1994

Max current draw for:

1989-1993 = 26mA.
1994 = 16mA.

If current is over 100mA then most likely a relay issue. Pull relays and see if draw drops
If current is over 500mA then most likely a switch issue.

deep_uv

Excellent point about the relays. Unfortunately, I had no luck with that either. Even checked the fuses and relays in the engine compartment.

I'd be happy to just get to 50mA. As I said earlier, I can last 3-4 weeks at 120mA draw so it's tolerable.

jjbunn

Update: solved!

Instead of removing the bulb from the under-hood light, I clamped the small switch nearby (which disables the light when the hood is shut), and the current draw dropped to 30mA i.e. normal!

That switch must enable the security alarm, or something, so holding it closed (open circuit) is how it should be when measuring the current draw from the battery.

Thanks for all the suggestions and input.