Battery Drain/BECM Question
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Thread: Battery Drain/BECM Question

  1. #1
    FRESHMAN ROVER
    Join Date
    September 12th, 2006
    Location
    Manchester, UK
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    108

    Battery Drain/BECM Question

    Does anyone know what amperage should be drawn once the BECM shuts down?

    I'm having a battery drain problem having just replaced the battery.

    When the car is unlocked, I measure 3.85amps for a few seconds, then it drops to 0.8amps. When locking, it remains at 0.8amps for 2 minutes until the BECM shuts down, and then drops to 0.25amps. It continues to draw 0.25amps from then on. Is this a normal load once the BECM has shut down?

    Thanks
    current: 2004 4.4 Vogue LPG (BRC sequential)
    sold: 2000 4.6 Vogue LPG (BRC sequential) (bought at 88k, sold at 176k)

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  3. #2
    FRESHMAN ROVER
    Join Date
    June 4th, 2007
    Location
    Chorley, Lancs. England
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    Re: Battery Drain/BECM Question

    My BECM drops to approx .15 but it sounds like your alarm reciever is picking up spurious RF signals which is waking the BECM up therefore causing the battery drain.
    Try searching as there have been many posts covering this issue plus see the sticky at the top of the page
    P38 4.0SE AUTO (95 model )1998
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  4. #3
    Premium Member
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    Re: Battery Drain/BECM Question

    The correct sleep current is 20-30mA - 0.020-0.30A. this should happen at around 2 mins 15-30 secs after the last activity.The key needs to be out of the ignition switch and the doors need to be closed.(Bonnet open is OK for this test.)
    Think beyond -

  5. #4
    FRESHMAN ROVER
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    Re: Battery Drain/BECM Question

    Thanks for the responses...

    I don't think I've got a problem with the BECM waking up. Once it has shut down after the 2 mins, it draws a constant 0.18amps-0.25amps (180-250mA). Unlocking starts up the BECM where it draws 3.8amps for a short while and then rests at 0.8amps (800mA) where it stays until the car is locked again and the BECM shuts down.

    The problem seems to be more about the load that is drawn in shut-down mode. 250mA is way higher than the 30mA allyV8 says it should be.
    current: 2004 4.4 Vogue LPG (BRC sequential)
    sold: 2000 4.6 Vogue LPG (BRC sequential) (bought at 88k, sold at 176k)

  6. #5
    SENIOR ROVER q-rover's Avatar
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    August 14th, 2007
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    Norway
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    Re: Battery Drain/BECM Question

    Try this, at least it will tell you if the BECM is sleeping:

    This test will determine if the BECM goes to sleep properly or it will stay awake.

    1. Sit in the vehicle in the driver seat with all the doors closed.
    2. Wait until the interior light switches off.
    3. Switch on the ignition.
    4. Switch off the ignition.
    5. Open the driver door and leave the door open for the reminder of the test.
    6. Switch off the interior lights by pressing the button for 4 seconds. On the message centre you can observer the message "Lights off".
    7. The message centre displays "Ignition key in" for approximately 2 minutes.
    8. If the display goes blank after the two minutes, then the BECM is gone to sleep, if the display is still on, then the BECM did not go to sleep.
    1998 Autobiography 4.6 V8 of course

  7. #6
    Premium Member
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    Re: Battery Drain/BECM Question

    Quote Originally Posted by Zebedee
    Thanks for the responses...

    I don't think I've got a problem with the BECM waking up. Once it has shut down after the 2 mins, it draws a constant 0.18amps-0.25amps (180-250mA). Unlocking starts up the BECM where it draws 3.8amps for a short while and then rests at 0.8amps (800mA) where it stays until the car is locked again and the BECM shuts down.

    The problem seems to be more about the load that is drawn in shut-down mode. 250mA is way higher than the 30mA allyV8 says it should be.
    If you are happy the BECM is sleeping then the first thing I'd do is to disconnect one by one any extra kit the car has fitted - I notice you have LPG,this ECU is one possible cause.Old mobile phone kit is the usual suspect tho....
    Think beyond -

  8. #7
    FRESHMAN ROVER
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    Re: Battery Drain/BECM Question

    The technique I used for measuring load was:

    a) disconnect the negative lead from the battery
    b) connect an ammeter (the 20A connection on the voltmeter) in line between the negative lead and the negative terminal on the battery
    c) closed the bonnet (because I thought the BECM wont shut down with the bonnet open)
    d) re-synked the key by pressing lock on the fob and then turning the key to left in the drivers door
    e) unlocked the central locking using the fob
    f) double locked the central locking using the fob - I timed the BECM shut-down on the ammeter and it was almost exactly 2-mins.

    The only things that could draw load (other than the factory fit items such as the alarm) is I've added an LPG and a phone kit. I guess it is one of these 2 that is drawing the extra 220mA.

    The problem first started because I hadn't used the car for a few weeks and the battery was flat (battery only about 2-months old). It's gone flat a few times since then. However, I'm now thinking that this is a starter motor or earthing problem because this morning it wouldn't start because of what seemed like a flat battery. Tried again and same problem. After about 2 minutes, tried it again and it started normally and seemed to have a full battery. Tried it again at lunchtime and did the same again. The only odd thing was the clock had stopped from this morning as if it was a flat battery, and is now working again.
    current: 2004 4.4 Vogue LPG (BRC sequential)
    sold: 2000 4.6 Vogue LPG (BRC sequential) (bought at 88k, sold at 176k)

  9. #8
    NEWBIE
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    February 5th, 2012
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    Re: Battery Drain/BECM Question

    I know this is an old thread but I'm hunting for answers as to why my baby is struggling so much now. I did try the following as I'm having significant issues getting through a 24 hr period or less without the battery going from full to flat.
    So I did the below to the letter but my question is the last step when they say after approx 2 mins the display should blank to show your BECM is asleep. After 2 mins I find that the screen blanks the dash beeps three times and the warning message Key in redisplays. If you leave everything this happens again in 2 minutes. So the question is, is this right or do I have an insomniac BECM?

    Many thanks

    Tim
    Quote Originally Posted by q-rover View Post
    Try this, at least it will tell you if the BECM is sleeping:

    This test will determine if the BECM goes to sleep properly or it will stay awake.

    1. Sit in the vehicle in the driver seat with all the doors closed.
    2. Wait until the interior light switches off.
    3. Switch on the ignition.
    4. Switch off the ignition.
    5. Open the driver door and leave the door open for the reminder of the test.
    6. Switch off the interior lights by pressing the button for 4 seconds. On the message centre you can observer the message "Lights off".
    7. The message centre displays "Ignition key in" for approximately 2 minutes.
    8. If the display goes blank after the two minutes, then the BECM is gone to sleep, if the display is still on, then the BECM did not go to sleep.

  10. #9
    JUNIOR ROVER
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    April 30th, 2005
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    Alton Hampshire UK/Cape Town SA
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    932

    Re: Battery Drain/BECM Question

    You have a faulty ignition key detector.You should not get the message "key in ignition" when the key has been removed.I presume you are doing the test with the key removed?.Try putting some graphite powder in the ignition switich and afterwards insert and remove the ignition key several times.After this you should no longer get the "key in ignition " message with the key removed and the Becm should go to sleep with a current drain of 30ma.
    John W
    1995 4.6hse
    Enjoy it!!

  11. #10
    NEWBIE
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    Re: Battery Drain/BECM Question

    Quote Originally Posted by John W View Post
    You have a faulty ignition key detector.You should not get the message "key in ignition" when the key has been removed.I presume you are doing the test with the key removed?.Try putting some graphite powder in the ignition switich and afterwards insert and remove the ignition key several times.After this you should no longer get the "key in ignition " message with the key removed and the Becm should go to sleep with a current drain of 30ma.
    Hi John,

    thanks for the quick reply.
    No, I am doing the test with the key in the ignition. The previous poster which I quoted suggests that with the key in the ignition after two minutes the display will blank even with the key still in there but I wanted to check is this was actually the case or not as clearly after 2 mins it blanks and then beeps and says key in ignition which is accurate (it is) but I was trying to find out whether it should actually just blank and not warn about the key anymore if the becm has gone to sleep. Can anyone have a go and let me know what happens?

    Regards

    Tim

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