Monday, September 16, 2024

Weird battery drain on the 911

For the past few months I noticed something odd, every now and then I'd have the 911 on my CTEK charger but it'd throw an error that the battery wasn't holding charge. I figured that my battery was just dying but it's really only been 3 years. Still after the battery just wouldn't charge anymore, I bought a brand new battery and noticed the same thing was happening. I decided to check for any draw on the battery while the car was off and key out of the ignition and it measured 370mA. That's way too high especially for an "old car" with barely any electronics.

370mA of draw

I unplugged every fuse and relay from the car and nothing changed. This was bizarre. I eventually gave up and took it to Lee's Autowerks so he could get to the bottom of it. He eventually found the source of the problem but it wasn't the usual suspects. For whatever reason, the ignition switch had become faulty and the contacts terminal 30 and terminal X was closed (on) all the time. You can see in this video comparing it to the a new ignition switch (later installed in the car) that those contacts should be normally open.


Faulty ignition switch (left) vs new normally working one (right)

With the new ignition switch install and key out of the car, you the draw is now only 35mA which is well within the 100mA max static draw noted in the service manual. Big thanks to Lee for getting this all sorted so I don't have to worry about the battery just dying on me if it's not on a tender all the time.

35mA static draw with the new ignition switch

Maintenance Update:

Mileage: 173,397

- New ignition switch