Troubleshooting Battery Drain

I�m trying to locate the culprit that is draining my battery after I shut off the car. With the driver�s door and frunk open, current draw is 80-90 ma. Going through the fuses one by one, I found that D1 (power window front) draws about 20 ma and E2 (CU memory M537/M538) draws about 25 ma. Are these numbers common? Where do I go from here with this information? Thanks.

Ignition switch

From your short, quick reply, it sounds like this has been a common problem solved by many. Would a bad ignition switch cause both current draws (windows and CU memory)?

When the electrical gremlins strike, replacing the ignition switch almost always solves the problems. It is a good place to start. Make sure you double check the part number, there are different electrical ignition switches depending on year.

Thanks. It looks like an inexpensive way to start.

To test for battery drain :: 1 open drivers door and latch door latch (to simulate a closed door) 2 open frunk and latch frunk latch (to simulate a closed frunk) 3 start car and run all electrical equipment , radio, windows, sunroof, a/c ect. 4 turn off key and remove key from switch 5 connect suitable amp meter( that can read from milliamps to 15 amp) from battery negative to body ground 6 remove ground cable from body ground ( all current is now going from battery through amp meter to body ground) analysis ::: current drain will be high for the first few min (5-10 amps) but will decrease rapidly as control units turn off (even more rapidly if the car is locked ) and should be down under 50ma in 5-10 min (usually in the 30ma range) NOTE ;;on some 996 Turbo models the instrument cluster will not go to sleep for an hour) if the drain after an hour is over 50ma diagnostics are required. Diagnostics:: With amp meter reading the current draw, start disconnection the power source to various components/ control units until excessive drain circuit has been identified ( indicated by the amp meter showing under 50ma) Hope this helps !!

I thought I was there already. But my method differed from yours in perhaps a significant way: I didn't latch the driver's door or the frunk before doing the diagnostics. So what I did did not rule either of these out as far as a long-term draw. That said, ... I started my troubleshooting after the car had been off for a few days. I removed the battery grounding cable from the body ground and inserted my ammeter in series between the battery and body ground. The power draw stabilized at about 81 ma. I disconnected power source to the various components (i.e., pulled individual fuses) one at a time. Most times the ammeter reading did not change. On some, the ammeter reading fluctuated a bit but returned to about 81 ma. Through this process, I identified two "drainers" - D1 (power window front) and E2 (CU memory M537/M538). With these disconnected, the power draw dropped to about 36 ma. 808Bill and DBJoe996 have pointed me to the ignition switch (thank you). I'll give that shot because it sounds inexpensive and not so time consuming. Any other ideas for where to look?

It's very important to simulate closed doors and closed frunk. It's also very important to hookup amp meter BEFORE disconnecting the ground cable so no interruption of current. ( interrupting the current flow will sometimes temporarily cure a drain that will only come back after component/control unit is exercised ( put in service for a period of time then turned off) Using my method exclusively will help find "intermittent" drains that can occur, and also will keep from misdiagnosing drain problems.. diagnosing battery current drains especially intermittent ones, can be very difficult/complicated. your method MAY work for this one, but is not a reliable method to use.

Got it. I'll give it another go using your procedure.

Porschetech 3-Do you mean turn on things like the radio and blower and leave these on as you turn off the ignition key, or just turn on then off before shutting the engine off?

Quotes source post: 17506117

Under normal circumstances on a properly functioning electronics, either way SHOULD NOT result in an excessive battery drain above 50ma, BUT when troubleshooting an erratic intermittent current drain BOTH should tried if one doesn't produce the fault. That's why I always use/turn on/off all the electrical systems before doing an current drain test and NEVER interrupt the circuit before the test can be done. Explaining the why's and how's of troubleshooting electrical gremlins can get as complicated as the actual troubleshooting/tests.