14 replies to this topic

[Joncole21]

Hi,

I have a 1999 MPI mini cooper. I am having problems with battery drain when the car is not used daily. I have had the alternator and battery checked out at my local garage and checked them myself and both are good. With the engine running I get around 14.15 volts at the battery. The battery is only about a month old and this problem was there before the battery was replaced.

I have been checking the battery voltage for the last 2 nights. The first night I left the battery connected and the reading last thing was 12.64 volts, the following morning this had dropped to 12.19 volts.

The following night I did the same check, but removed the battery earth lead over night. The readings were 12.85 volts in the evening and 12.67 volts this morning.

I have used a meter to check the battery drain and this appears to be a constant 140mA. I have then checked every fuse one at a time and the only drain i could find was connected to the alarm, radio and clock (C4) and this only measured around 9mA. I have removed all the fuses from the inside fuse box and still read a drain at the battery of 130mA.

Does anyone have any suggestions where or what to try next?

Thanks

[tommy13]

130 ma is certainly too much. Try disconnecting the wires on the alternator and see if it drops, it may be charging but it could also be draining the battery when the engine is not running.

[Bungle]

your doing everything right so far but can't thing of anything else to try

maybe the multi plugs by the steering coulomb

[Sprocket]

humor me and remove the dim dip relay. while i've not measured the drain current, I have measured a resistance from +ve to -ve with everything switched off and the battery disconnected, which turned out to be the dim dip relay.

[tommy13]

You may also try disconnecting the main relay which is under the bonnet (oblong black box) attached to the brake servo bracket. I found this to be the problem on a Rover 100 with the same problem. Both vehicles use the same relay.

[Sprocket]

Good call! Some cars have been found to hold the main relay on after the engine is shut down. Can't remember wht the real reason was, but its deep in the injection section somewhere.

[Samini86]

Its probably the cold weather, mine does the same when its cold!

[miniman retford]

Had the same problem with mine last year, turned out to be a broken wire where the loom bends up onto the ecu.

[tiger99]

I know that a Metro has a power hold relay, which keeps certain systems (probably mainly the electric fan) powered up for a while after the ignition is switched off. Your Mini may have something similar, if so the current should go to zero if you wait for a while. Perhaps 10 to 20 minutes?

But as has been said, the alternator is always in circuit, and could have a leaky diode.

[xrocketengineer]

Good call! Some cars have been found to hold the main relay on after the engine is shut down. Can't remember wht the real reason was, but its deep in the injection section somewhere.

Well it happened to me but it is a SPI. It was resolved with a remanufactured ECU. Long story:

http://www.theminiforum.co.uk/forums/topic/119357-ecu-smart-failure/

[Joncole21]

Hi all, I have solved the problem. As suggested I started pulling relays and on disconnecting the second one the drain dropped to 25mA. The relay was for the front fogs. I assumed this was at fault but on testing appeared ok. I then checked the wiring diagram and found that the relay was wired incorrectly. The irony of this story is that I paid the garage I purchased the mini from to fit them as I wanted the job done properly.

[tiger99]

Well done! But where is the 25mA going? That is still enough to flatten your battery in approximately 2 to 3 months, depending on the size of battery you have fitted, and probably will be ok, but I am curious.

[Joncole21]

Hi tiger99. When I take out the following fuses C4,B4,A4 & B6 the drain drops to 10mA. The fuses I removed are for the alarm, radio and engine management. I cannot account for the remaining 10mA drain.

[stulewuk]

Hi, might seem a daft question but how do you set a multimeter to check drain off the battery? I am not usually one for electrical issues, but I have some at the mo and really need to resolve myself, without an auto elec being paid

[Bungle]

set the scale to DC amps

disconnected the wire between the battery and car body

now fit the multi meter between the negative terminal on the battery and the earth point on the body