Battery disconnect.

[RR330i]

I want to reboot my car's computer.
How do I disconnect the battery?
I know it seems like a silly question, but
it doesn't say how in the manual, and under the
hood is just a place to jump the car.
Or am I missing something? :?

[morcheeba]

No worry. Most people just assume that the 330i has a regular big bulky car battery, but it actually runs off a nine-volt located in the glove box. It's a lithium battery, so it should last 10 years.

Ok, I wish. The battery is in the trunk, on the passenger side, behind the wheel. The only trick to disconnecting the battery is remove the negative terminal first. The idea is that your wrench might slip and accidently touch the body. If you disconnect the positive side first, then the ground side is still connected to the body & you'll create a big spark (and that's it, if you're lucky). If you disconnect the negative side first and touch the body, then it's ok - it's already connected. .. once you get one terminal off the battery, you're safe (unless of course, you lay your wrench directly on the battery). To reset the car, you only need to remove one terminal (the negative one). You should wait a while (~30 minutes) before reconnecting to allow the computer to drain its capacitors and reset completely.

(sorry for the ramble, it's late after a long hot weekend)

[schnitzer]

FYI, if you have an alarm, once you discounnect the battery, it will go off for about 30 seconds.. because the alarm has a backup battery in case someone tries to unhook your battery.

[david]

does it really take 30 minutes? i've reconnected in 10 minutes and my computer seemed to be reset....

[morcheeba]

Sorry, I don't remember where I got that number. It's probably just pulled out of my ... uh, hat. Ten should be fine, too, but I really have no idea what size capacitors they have and how much current it takes to preserve the memory.

Back in the 80's, I would have said a few minutes because capacitor sizes were limited to about 0.01F and chips took milliamps to sustain memory... now you can buy a 10F capacitor that's tiny, and chips can sleep on a microamp -- if I did my math right, that would be 115 days.

[jake]

What is the benefit to rebooting the car's computer?

Thanks