Jump starting car makes alarm go off, help?

April 3, 2005 10:26 AM

My friend owns and 93 M. Benz 300E and it wont start. When he attempts to jump the car his alarm goes off... What can he do to fix this?
posted by crewshell to travel & transportation (5 comments total)

Try a new battery, but make sure you get one that has sufficient capacity to turn over the 300E's engine. Should be ~$50 at an auto parts store.

Also, try asking at Roadfly
posted by b1tr0t at 11:32 AM on April 3, 2005

Some car alarm systems don't take kindly to having the power die completely. If the alarm goes off right when you connect the batteries together, then keep the wires connected while you deactivate the alarm with the key. Usually this involves putting it in the ignition and turning it on, or unlocking and relocking the driver's door... see the manual to be sure.

Anyway, after you get the alarm to stop, you ought to be able to start the car then.
posted by odinsdream at 12:03 PM on April 3, 2005

Usually this involves putting it in the ignition and turning it on

I've never tested my alarm thoroughly (for obvious reasons) but I second this statement. I once locked my door from the outside and left someone inside. They opened the door and the alarm went off. Just turn the key one notch, which should disable the steering lock and alarm system, and try again. If that doesn't work, take it to the dealership.
posted by SeizeTheDay at 12:31 PM on April 3, 2005

I wouldn't buy a new battery before you check the alternator. It should be charging about 13.8 volts. A perfectly good battery will discharge if the alternator brushes are worn. I have a 300 Turbo Diesel, and recently had this problem. The regulator/brushes assembly was only $15, and changes with two screws. The E class may be different. Google Groups is a big help. BTW, Never jump start a battery unless you make the final negative connection to the engine or frame of your car, away from the battery. Hydrogen gas plus spark can explode batteries.
posted by weapons-grade pandemonium at 6:58 PM on April 3, 2005

My BMW has an ignition cutout that activates when it thinks it's about to be stolen. Restarting the car after that requires the original key and some arcane series of steps, including, I think, a code entry.

Don't know if that's what happened to your friend, but it sort of sounds like it.
posted by ikkyu2 at 10:35 PM on April 3, 2005