Alarm going off / parasitic power draw

Totally possible, yes. I have had this before (a faulty amp causing battery drain) on an e46 (same electrical system), and also know if you disconnect the battery with the alarm armed, the alarm will sound

So yes, battery voltage dropping will trigger an alarm
 
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I was going to say this will be a battery issue- fully charge the battery or replace it and the issue should be resolved including the key remote working again. I had this on mine even though the old battery was on a trickle charger it was not ever fully charged. New battery solved the issue.
 
Battery is less than 6 months old. Was replaced not long before I bought the car, i guess someone replaced it thinking it was the issue before I bought the car.

Using suggested techniques to identify parasitic drain of putting a multimeter in series to the battery, I've found the car even long after it should have gone to sleep keeps drawing 0.4A / 400mA. Whereas an expected draw should be under 50mA.

Checking fuses, I seem to have around 150mA draw through fuse 45 which is marked as for the airbag. However pulling that fuse I still measured a draw of 400mA from the battery. So I'm now struggling to work out where the draw is coming from!

Any suggestions welcome!
 
Nellybauer said:
Battery is less than 6 months old. Was replaced not long before I bought the car, i guess someone replaced it thinking it was the issue before I bought the car.

Using suggested techniques to identify parasitic drain of putting a multimeter in series to the battery, I've found the car even long after it should have gone to sleep keeps drawing 0.4A / 400mA. Whereas an expected draw should be under 50mA.

Checking fuses, I seem to have around 150mA draw through fuse 45 which is marked as for the airbag. However pulling that fuse I still measured a draw of 400mA from the battery. So I'm now struggling to work out where the draw is coming from!

Any suggestions welcome!
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Do a voltage drop check on each fuse instead of amp draw. When you pulled the fuse you probably woke up another module on the network.

 
BumpyZ4 said:
Do a voltage drop check on each fuse instead of amp draw. When you pulled the fuse you probably woke up another module on the network.

Click to expand...

Sorry I should have clarified before, the method you suggested is what I used. Let the car go to sleep with the door latches pulled. Confirmed then that still pulling 400-430mA.

Using the method as you suggested, checked all fuses for voltage drop, fuse 45 shows a drop of 1.1mV, which according to the chart for a 10A fuse is 143mA - not the full ~400 I am losing.

Then removing fuse 45, again ensuring car still asleep, continues to still have a draw from the battery of 400-430mA.
 
Turned out my multimeter was buggered, annoyed at myself for that as wasted a lot of time! So now armed with a new 1...

The fundamental is still the same, just the power draw was wrong. After leaving the car for 20 mins, I have a power draw of 170mA.

This is with my GM5 disconnected as I'm sending it off to get relays repaired, so that would likely be adding a bit more on top of the 170mA.

Fuse 45 has a voltage drop of 1.1mV which equates to 143mA, so does look like it could be the entire excess power draw?
Removed fuse 45, got an immediate spike back to ~800mA as must have awoken something else. Let the car go back to sleep/steady state and overall power draw has dropped from 170mA to 140mA. So seems even with that fuse out a module or something is still staying powered up.

Any modules fuse 45 interfaces with but may be getting direct power outside the fuse?
 
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I’m late to this thread, but I can confirm that:
- low battery state of charge results in the alarm going off
- locking the car with the key by turning it in the lock direction three times (without unlocking it between turns) locks the doors without setting the alarm
- a bonnet sensor fault is a common cause for the alarm going off
- parasitic drains are a PITA

I have an intermittent parasitic drain that sometimes flattens the battery in a few days and at other times isn’t there for weeks. I keep mine on a trickle charger now.

My alarm goes off at random but locking the car as I described prevents this.

I had both of these problems on an E46. In that car, disconnecting the bonnet sensor and replacing the hedgehog resistor solved both.
 
BMWZ4MC said:
- locking the car with the key by turning it in the lock direction three times (without unlocking it between turns) locks the doors without setting the alarm
- a bonnet sensor fault is a common cause for the alarm going off
Click to expand...
Can also lock with tke key button, then press it again straight after which engages the alarm but not the movement sensor inside which I found seemed to be helping a bit with mine. Also have left my bonnet sensor disconnected.

I'm working through more troubleshooting, seeing what ChatGPT can suggest as the next steps - not tha tI hold out much hope :) Maybe hedgehog resister is next...
 
Look for any aftermarket "stuff" that may have been added to the car. It may have been tapped into this circuit on the power side of the fuse.
 
Check fuse F100, this is where fuse 45 gets it power from, by the battery for corrosion to make sure corrosion is not bridging two or more circuits. Probably not but only takes a few minutes to check.F100.JPG
 
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