Hi all, (second time writing this, internet explorer decided to stop responding as i was finishing writing! )

Right, ive had a battery drain problem with my P38 since ive had it, never really had much of a look into it untill today (working through list of faults in prep for selling, probably won't want rid once they're all done! )

i have read just about every thread on here about battery drains, so please don't shout at me for not searching, i'm sorry if i missed something.

Basically it seems my Becm is not going to sleep (tested using sequence described on BBS website) mine is a manual so i don't have a park light which seems to stay lit on the autos.

i have checked current draw today, and is as follows:

unlocked, ign off =1A
instantly after locking=.7A
about 10sec after locking=.5A

then stays constant at .5A.

A couple of times it has dropped to .04A which is about what i would expect, but there didnt seem to be any pattern to when it did drop down.

have tryed with:
Rf aerial lead unplugged
Rf unplugged completely
EAS delay relay unplugged
Volumetric sensor disconnected
alternator disconected
Air con compressor disconnected (found a random thread on here where someone said this cured theirs).
Each fuse removed one by one (radio/clock fuse made a slight difference as expected but not the full amount) only others to make a difference was 3 maxi fuses supplying Becm.

what other things can keep/wake the Becm up?

When the current draw is about .5A there is a very hich pitched noise from the Becm, probably just from the various IC's etc being live, as soon as the current draw drops to .04A the noise goes.


i don't really want to send the Becm off, partly because of cost and partly because of the inconvenience.

all suggestions welcome!
Adam

IC's do not make a noise. I would suspect that one of the relays in the BECM is vibrating due to either a fault in the BECM electronics or an external signal, bad connection or bad earth.
The fact that the noise goes and the current drops will not be a coincidence.

Did you try the wipers (headlights) apparently if their not parked properly that can drain

will try disconnecting headlight wipers tommorow, thanks
@Data. its much higher pitched than relay, and very very quiet. can only be heard with lid off Becm.

Have you tried removing the plugs to the Becm one by one till the noise stops then look at what that plug serves and your onthe right road to solving your drain.

aniesigh said:

will try disconnecting headlight wipers tommorow, thanks
@Data. its much higher pitched than relay, and very very quiet. can only be heard with lid off Becm.

Click to expand...

IC's do not make a noise. Small relays certainly can and depending on the frequency of whatever is driving the coil the pitch can be very high indeed. Transformer coils can also vibrate as can choke coils, can't think of much else in the box that would produce a noise

On closer inspection/listening with a fresh head it does seem to be coming from the relay end of the board and could actually sound like an energised relay although when power to board cut there is no sound of a relay de-energising :s it doesn't seem very practically possible to access the underside of the top board with everything still connected to probe around and see which relay has power to the coil. Anyone got any bright ideas? Tried pulling multi plugs 1 by 1 but none of them made it stop.
Oh also tried headlamp wipers unplugged with no luck,
Regards, Adam

oh and if i remove the top board, is anything going to loose its sync etc? i'm not worried about windows/radio etc.

one of the transistors is burnt out, not sure what its for. there is an external relay been mounted in there at some point, not sure if its been added to replace the burnt transistor.
is there a diagram anywhere showing which transistors and relays do what function? have looked around but not found anything.
Adam

aniesigh said:

oh and if i remove the top board, is anything going to loose its sync etc? i'm not worried about windows/radio etc.

one of the transistors is burnt out, not sure what its for. there is an external relay been mounted in there at some point, not sure if its been added to replace the burnt transistor.
is there a diagram anywhere showing which transistors and relays do what function? have looked around but not found anything.
Adam

Click to expand...

If you have a burnt transistor and bits have been added, it sounds like you have a major problem You need to talk to Rick the Pick, it may be recoverable, or you may need a replacement

i will PM him, the more i read Becm threads the more his name pops up. not convinced about it being a major problem, pretty much everything in the vehicle works i just have the battery drain problem although i don't think its related. i wouldnt have thought the transistor has any bearing on the Becm going to sleep which it isnt at the moment.
Dont really want to be into replacing the board to be honest.

Fixed it,
for anyone interested to know....

I had another look earlier and realised i had missed the plugs under the fuse board fixed to the Becm. pulled out connector C257 and the noise from board stopped and current draw dropped to .04A. now i was getting somewhere!

Quick look on Rave and all the wires to c257 are inputs, various lights etc.
Tested them all, none were directly connected to earth although two had a resistance of about 1800 ohms to earth. all the inputs are switched earths.
checked again and it turns out pin 9 has a live feed to it. this is the input for sidelights on, but when the switch is activated it returns to being an earth as it should :S
so as a quick/cheap/functional but not ideal fix, i cut the wire and put a relay in which effectively breaks the wire when the ignition is off. downside is it means i have no sidelights with ignition off. plus side is i have a Becm that sleeps down to .04A current draw within 2mins of being switched off!

i will look at the light switch at some point, maybe it could be a small problem with that causing the problem, cant see how else its happening but not sure if the light switch has a live feed to it. will look more into this in the next day or so

Adam

Good one