Battery Drain

[watuszak]

Hello everyone I have a 2003 325ci. My car battery has been draining weirdly, if I let the car sit for 12 or so hours, it will be dead. I have been unplugging my negative battery terminal everytime I leave the car to avoid my car dying, on my instrument cluster with the car off the battery voltage test said it was at 10.3 volts, I have it charging right now. I believe my final stage resistor is going bad due to fluctuating fan speeds when I drive and runs when the car is off, which is what I think causes the battery to die, but I'm reading various conflicting things online, anyone have suggestions?


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[TonyAngel]

The first thing to do is to confirm that the battery is good. How old is the battery? After 3 years, death is coming. Charge it overnight, check the voltage. Fully charged it should be at around 12.6v or just over (at under 12v, your battery is dead). When running it should be at around 13.7 or so volts. Under load it should be able to sustain right at around 10.5v.

At 10.3v the battery is dead, dead.

As for the fan, I thought they were supposed to vary their speed according to need and ours stay on for a bit after turning the cars off.

[watuszak]

The first thing to do is to confirm that the battery is good. How old is the battery? After 3 years, death is coming. Charge it overnight, check the voltage. Fully charged it should be at around 12.6v or just over (at under 12v, your battery is dead). When running it should be at around 13.7 or so volts. Under load it should be able to sustain right at around 10.5v.

At 10.3v the battery is dead, dead.

As for the fan, I thought they were supposed to vary their speed according to need and ours stay on for a bit after turning the cars off.

Should I be trusting the obc reading of the battery voltage or use a multimeter?


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[randy72877]

Replace the final stage resistor that is the problem. Charge the battery and test the voltage again. The blower motor should never stay on after the ignition switch is off. Battery discharge and erratic blower motor function are the classic symptoms of a bad fsr. This problem affects every bmw that uses the same fsr (e39, e46, and e53)

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[TonyAngel]

Dang, I don't know why I was thinking fan motor after reading the original post. Sorry, but randy is right. Get rid of the cause of the battery drain then put the battery through its paces. I always just use a DMM, but I'm new to BMWs and am not familiar with all that a dedicated scanner can do.

[mickfrommelb]

my problem is similar changed 2 final stage resistors, no difference .i think the problem is elsewhere

[jclausen]

You need to do a draw test. If the car has an automatic transmission you can check to see if the car is going to sleep. When you turn off the car and lock it, the "p" light at the top of the shifter will remain lit for up to 20 mins. Then go out, it the car does not go to sleep the light will remain on, meaning some thing is keeping the car awake. Or if the light went out then you checked later and the p light came on then something woke the car she up.

[watuszak]

You need to do a draw test. If the car has an automatic transmission you can check to see if the car is going to sleep. When you turn off the car and lock it, the "p" light at the top of the shifter will remain lit for up to 20 mins. Then go out, it the car does not go to sleep the light will remain on, meaning some thing is keeping the car awake. Or if the light went out then you checked later and the p light came on then something woke the car she up.

What if I have a manual transmission?


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[randy72877]

What if I have a manual transmission?


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No indication. Just wait 16 minutes and then it should be asleep.

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