View Full Version : Important: Read This Before You Jumpstart Your E30

07-30-2004, 02:00 AM
"Jumpstarting should be no problem if one important precaution is taken. Irrespective of which end of the jumper leads the BMW is on ALWAYS turn on headlights and heater fan before disconnecting the jumper leads. This is to damp out any possible surges caused by suddenly removing a load from a charging electrical system. This is to avoid a voltage surge when the load is removed from the electrical circuits which is the major cause of blown DMEs.

This applies irrespective of whether the BMW is starting someone else or being started itself."

Giga Shadow
07-30-2004, 05:32 AM
Wierd, I've jumped my cars many times. No problem so far...
Good to know! You can never me too cautious. :o

07-30-2004, 11:08 AM
Weird. Never done that before.

07-30-2004, 11:22 AM
There is no way I ever have the head lights or the heater fan off in my car(s). I know no place except France where people can legally drive with their headlights off in daylight.. :)
I don't know if there is a difference between US and European BMWs, in that the headlights aren't automatic in the US (always on, controlled by ignition key switch). My heater fan is always on lowest power mode all the time.

Good to know in any case.


07-30-2004, 09:01 PM
I saw a couple guys on the forum that recently jumpstarted their cars, so I figured it may have had something to do with them not following the directions above. So now, people know the right way.

BTW, I have to manually turn on the headlights in the e46.

07-31-2004, 12:29 AM
Usually it's the big OBC units (they'll say PPPP on the screen) and the ABS protection relay that get fried before the DME, but it's true you should turn everything on before you disconnect.

08-24-2004, 02:45 AM
Didn't someone recommend turning on the defroster too?

08-27-2004, 03:04 AM
You'll want to turn on as much stuff as you can right before you disconnect the battery cables. I think this is even in my owners manual. 8)
Any voltage spikes will absolutely kill your ABS relay and possibly fry your ECU. :oops:

08-27-2004, 03:15 AM
Kind of lame.. i've never heard this being an issue with other cars.

I never jump started anybody's car with my old e30 except maybe once or twice for my other bmw for this very reason.

08-27-2004, 11:34 AM
I wonder if this technique should be used in any car you own.