Z3 has on and off 170mA electrical drain

[Craig P Steffen]

Hi folks,

Short version: what thing on a Z3 pulls 140mA and cycles on for one minute and then off for one minute, continuously? I have a friend whose Z3 is having battery drain with this characteristic.

By the way, I'm looking for someone who has experienced (and ideally fixed) this very specific problem. I don't need general overview about batteries, or voltage, or grounding, or looking for leaks. (I appreciate that, but if I get 20 people telling me how to hook up an ammeter it will be difficult to find the specific information.)

2000 Z3 Roadster (the convertible not hard top). 2.3 L engine, manual trans. Battery in the trunk.

I'm helping a friend track down an electrical leak. Several car people (and I think at least a semi-pro mechanic) have looked to no avail. I put an ammeter between the battery and the chassis and pulled fuses to isolate it to one circuit. It's circuit #31 (5A fuse), which in the fuse cover is listed powering the following items:

- antitheft system
- Clock
- Electronic Immobilizer
- Exhaust gas diagnosis
- instrument cluster
- on-board computer

I was hoping it was the clock. I pulled the radio last night, got down to the clock, and pulled the three-conductor cable off the clock. It wasn't that; leak still there.

The behavior of the leak is the following. When monitoring the drain by putting an ammeter between the battery negative and the chassis, it cycles between about 25 mA and 170 mA. Almost exactly one minute at the high current, and then one minute at the low current. (My best estimate is 57 seconds on, 57 seconds off; I don't have a real precision electrical meter so I don't know what the real sampling rate is.) Having removed the radio, the leak is now down to about 5 mA, so I think most of the 25 or 26mA quiescent drain is the radio itself.

Anyone every seen anything like this? I would think it would be very specific if you had.

Thanks for any information. Sincerely,

Craig Steffen

 

[the Nefyn cat]

Does "anti theft system" include the alarm? Not entirely sure, but my alarm (when it goes off) seems to sound for about a minute or so and then shut up. Just a thought. If someone in the past has disconnected the siren just to shut it up then that may be something to do with it.

 

[NZ00Z3]

Hi Craig

The Z3 has about a 40 mA drain as standard to account for all the items you list under fuse 31. This is when the car is in sleep mode. Are you letting the car enter sleep mode when doing the testing? It takes about 10 minutes of no operation or door openings.

The batteries on both of my Z3's last about 2 weeks and can still start the car with the 40 mA drain. They don't last 3 weeks

 

[Craig P Steffen]

Does "anti theft system" include the alarm? Not entirely sure, but my alarm (when it goes off) seems to sound for about a minute or so and then shut up. Just a thought. If someone in the past has disconnected the siren just to shut it up then that may be something to do with it.

Oooh--that's a thought. You're the first person I talked to that had a hypothesis that actually has a time element to it.

And someone else I talked to today suggested testing the alarm system just to see how it functioned, and if that made any difference. Sounds like I need to put that on my list for testing.

 

[Craig P Steffen]

Hi Craig

The Z3 has about a 40 mA drain as standard to account for all the items you list under fuse 31. This is when the car is in sleep mode. Are you letting the car enter sleep mode when doing the testing? It takes about 10 minutes of no operation or door openings.

The batteries on both of my Z3's last about 2 weeks and can still start the car with the 40 mA drain. They don't last 3 weeks

Thanks for the info.

Hmm. Yeah, in this Z3, with fuse 31 removed, the drain is about 26 mA. With it in, the drain cycles between 26mA and 170mA. So what I'm assuming is that 26mA is what it *should* be and 170mA is something on that only should be on when the car is running, or something. With the on/off higher drain the battery barely lasts a week (this is reported to me, but by two people, both of whom are reliable about that sort of thing.).

Thanks for the ping about sleep mode. I will be careful about that. I will also report back.

 

[Stevo7682]

If you are looking at the alarm being a possible root cause the 2 main things to look at that could commonly cause false alarm activation are the bonnet alarm switch at neardide headlight or boot wiring loom your drain could be the alarm triggering but the sounder may be turned off or faulty.
Stephen.

 

[Craig P Steffen]

A quick update. I've been investigating further. The periodic drain is in the instrument cluster, specifically, the center of the three connectors. With the instrument cluster removed, there's no drain.

 

[D R Oldfield]

Had a similar fault on a 3seriestouring it was a faulty rev counter that occasionally would kick when the ignition was off luckily I had spare just replaced it just out of interest are you using an analogue or digital ammeter because the damping on a digital metering always give a true reading at that level of current by the way my 3 series touring was showing a draw of about 150 mA but momemetary rising to 250 mA

 

[Kasey paramore]

A quick update. I've been investigating further. The periodic drain is in the instrument cluster, specifically, the center of the three connectors. With the instrument cluster removed, there's no drain.

Did you solve this problem? I have the exact same car and I am having the exact same problem. Battery totally dead after approx 4 days

 

[smiffy]

The closest I've got to solving this, on mine and another one I had a go at, is it is related to the stereo system.

In the end, I fitted a switch in the boot (trunk) in the stereo negative line. It's the brown wire that grounds under either one of the roof pump bolts or antenna mounting bolts.

Whilst the open circuit stops the drain, it also wipes the radio settings. Just have to flick the switch on before getting in the car, otherwise the stereo doesn't work!

 

[Tracy Dee]

Try pulling fuses .
Mine turn out to be fuse 8 if I remember correctly. it was only being used for the radio memory
The memory wire was redirected to the live cigar lighter which worked a treat and leaving fuse 8 out was the only way to stop the drain as fuse 8 served no other purpose happy it was removed after a year and 3 batteries later and a fair few people looked at.

All kindly diagnosed and fixed by smiffy

 

[smiffy]

Try pulling fuses .
Mine turn out to be fuse 8 if I remember correctly. it was only being used for the radio memory
The memory wire was redirected to the live cigar lighter which worked a treat and leaving fuse 8 out was the only way to stop the drain as fuse 8 served no other purpose happy it was removed after a year and 3 batteries later and a fair few people looked at.

All kindly diagnosed and fixed by smiffy

Followed by @Shelly 's sausage rolls!

 

[Shelly]

Followed by @Shelly 's sausage rolls!

It was a lovely day when we all met up

 

[CWP@Roadster]

I had a similar current drain, which was caused by a bad microswitch in the stricker plate. The alarm system aways thought the drivers door was open and never went to sleep. If this is the case, the overhead light will always be on in auto mode. My quick solution was to disconnect the switch behind the drivers seat. A new strikerplate/switch was expensive and out of stock at the time I addressed the problem.