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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > Disconnecting the Battery...

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      04-11-2006, 08:38 AM   #1
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Disconnecting the Battery...

I looked for other threads but didnt see any that addressed this issue. I am about to install the factory alarm myself, I know I should disconnect the battery, but I am wondering, when I go to reconnect it are my nav and radio going to work like normal? OR are there any security codes you have to put in? I didnt see anything in the manual about this. I just wanna know b4 I start.

Also I know I should, but does anyone really think it makes a difference if I DONT disconnect the battery to install the alarm? It seems like its all plug and play.
2008 335i: Platinum Bronze/Terra/Burl, Prem, Sport, Cold, I-Drive/Nav., Comfort Access, Logic 7, I-Pod/USB, Paddle Shifters, Alarm

2006 325i: JetBlack/Terra/Burl, Prem, Sport, Cold, Xenon, I-Drive/Nav., Alarm. - DECEASED (totaled by 19yo driver)
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      04-14-2006, 05:56 AM   #2
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Alarm install

A few observations about alarm install. When i reconnected the battery, the only thing I had to reset was the time and day. All my NAV and radio settings remained intact. Not sure you need to actually disconnect the battery, but I did anyway. I also was able to install the siren without actually removing the rear tire. I was able to jack up the car (and place 2 jackstands) and had plenty of room to remove the covering and install the siren without removing the tire.

Very easy install overall. The only thing that I got nervous about was when I reconnected the battery, there was an error message in the NAV window about the DSC being disabled and a 4x4! error message indicating limited driveability and warning me to get the car to a service center as soon as possible. Once I took the car out the next day, the message disappeared after one minute and never reappeared. Apparently when messing with the battery, this part of the system needs to reset itself by driving for a minute or so. The message will NOT dissappear simply by turning the engine on and off - which is what I did the day of the alarm install when the message would not disappear.
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      04-14-2006, 09:14 AM   #3
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As far as pulling the terminals off, Always pull the Negitive (ground) terminal off first (Unless you have a rare vehicle that is positively grounded). Then remove the positive terminal. This helps reduce several safety risks. One major one is if you remove the positive terminal first and your car has a negitive ground, if you contact any metal the wrench will short out. In my case about 22 years ago (When I didn't know all that much about cars) I did this and the battery exploded, splitting the battery open and sending acid all over. Not a fun thing.

As far as the other questions, I'm not sure of the recommended procedures for new BMWs.


BMW seems to suggest clamping in this order:

1. + of good battery
2. + of dead battery
3. - of good battery
4. - of dead battery

Then remove in opposite order.

Most places suggest the following order:

1. + of dead battery
2. + of good
3. - of good
4. - of bad

The remove in opposite order.

In both cases, remove from - terminal of dead battery first.

Also, most people will jump with the cables still attached, car with good battery still running. I read somewhere that in order to avoid the remote possibility of damaging the ?alternator of the bad battery car, you should turn off the good battery car and remove cables, then try starting the bad battery car. If that fails, then try the method most use and hope nothing shorts.


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      04-16-2006, 06:50 PM   #4
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When I installed my OEM alarm, I didn't disconnect the negative terminal to the battery.
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      04-17-2006, 06:58 PM   #5
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I disconnected the battery to install my light bulbs and a angel eye kit, just in case...

Arctic/Blk Leather/Alum.Trim/MT/ZSP/Sunshades/Blk Lines/M3 Illuminated Knob/Alcantara Performance Wheel/M-E-Brake Handle/Euro Fog Switch/Koni Yellows/H&R Sport Springs/19" VMR V718's w/PS2 Tires/M-Tech Body Kit/Carbon Fiber Spoiler/Bimmian Interior Bulbs/OEM Eye Glass Tray/SSK/Alcantara Boot/Split Armrest/OEM Dual Rear Power Outlets/Rear Ashtray Delete/OEM Alum. Pedals/Osram 6000K/Brex Rings/LED Side Markers/BMS Power Box
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