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Old 03-25-2020, 08:51 PM   #1
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Join Date: Jun 2013
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Electrical Issue 330i

Has anyone ever seen anything like this??

I had an electrical issue on my car in that everything was perfect - until stopping to get gas the other day; I got back in and it was no crank/no start though the battery was hot, dash would light up as normal, etc.

After some testing, I realized I COULD start it by jumpering the green and black/blue on the ignition switch to send power to the starter while turning the key. At that point it would start like a race car and everything was fine.

I only did that 5-6 times to get the car home, and in testing - to track the starting problem.

However the last time I did that, the dash went dark and everything seemed to lose power!

Now the dash is totally dead - even with the key on - EXCEPT when I turn the headlight switch to marker lights position. If the switch is in auto or off - and the dash is dead. If I turn the headlights full-on - the dash flickers and acts crazy for a bit, but then comes on full.

I could not find any burnt fuses (Ive specifically checked 10, 34, 43) - but am hoping someone can point me to one I've missed.

Also, the curious thing is - with BMW Scanner plugged in - the DME module shows "not responding" (along with several other modules -but not all) unless I set the headlights to on - and then it - and all the other modules present report in fine.

Does anyone have any ideas on what to test or check?

Thanks for any information,
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Old 03-26-2020, 06:56 AM   #2
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First, check the cable connectors at the battery. They have to be nice and tight. If youíre in the mood, remove the ground and then the positive cables. Use a 3M green scrubby on the battery posts and the inside of the cable connectors. Install the positive cable, then the negative cable (sparks are ok). Also, use a digital volt meter to check the voltage at the battery. A properly charged battery will show about 12.9VDC.

Next, pop the hood and check the voltage at the jumper post located under the red plastic cover. Use the engine for ground. The voltage needs to be identical to that recorded at the battery. There are 2 possibilities If itís low or zero. The engine ground strap is located under the car at the right front corner of the oil pan. The other end bolts to the chassis. The other cause if zero volts is the Battery Safety Terminal (BST). Thatís on the red positive cable at the battery. That blows (literally) when the car is in a crash.

Ok, letís say the voltage at the jumper post is fine. The post also serves as the connection for the cable to the battery and the fuse panels. There could be corrosion at the jumper post. Remove the ground cable from the battery. Then disassemble the jumper and clean any corrosion. Reassemble and reconnect the ground cable.

Lastly, the ignition switch (not the lock) could be bad. They do wear out. You can clean the contacts with a relay contact file and some electrical contact cleaner. Also, while youíre there make sure the switch rotated when you turn the key in the ignition switch. The lock (on the right side of the steering column) is connected to the contacts via a plastic shaft.
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Old 03-26-2020, 08:30 AM   #3
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You report that the battery was "hot". Not doubting you, but do you have prior experience as to how warm any battery under charge should be?

Past that...if indeed the battery was "hot" sounds like two possibilities.

A cell in the battery is no good and shorting, creating excessive heat.

The alternator is creating excessive output.

If the former, be careful. Any battery pushing out gases as a result of overcharging and/or shorted cell can sometimes go boom. It's rare but it does happen. Trust me (BTDT) you want NO part of a battery going kaboom.
If that's the cars, again rare be wary of making sparks around the battery until the area has had a couple of minutes to ventilate.
(Overly cautious, yes but the fumes of an overcharged battery can ignite with spark)

What's the battery voltage at rest, car running?
Whats the alternator output? Prefer amps, but we'll take voltage.

With the car running (?) what's the alternator output with the heavy consumers turned on?
Don Fields
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