Draining battery

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by COACH, Jul 26, 2013.

  1. COACH

    COACH New Member

    Does anyone know what could be running my battery down? Something is still running while the motor is cut off. The battery is almost new (red top)...if I do not crank the truck for several days the battery will be down to 50-60%...the only thing that I know running is my Garmin Vista....even when that is unplugged the battery still goes down....the battery charges quickly....thanks!!
  2. j cat

    j cat Epic Member 5+ Years 1000 Posts

    battery drain is things like a glove box light or other lights on. also it could be the alternator with a bad regulator that is with a leakage to ground.
  3. jake's silverado

    jake's silverado Epic Member 5+ Years 500 Posts

    On my impala the car seemed to wake up. Turned out to be a bad BCM. This is a tricky one to find. I started pulling fuses an monitoring. Eventually lead me to the BCM. Hope this helps a bit but sounds like a bit more trouble shooting. So I hooked up a multimeter and found out what what the normal draw on the battery was then in about 10 to 15 mins it seemed to jump up to like 320 milliamperes from about 40 if my memory is correct. Then one by one eliminated circuits.

    Good luck.
  4. With key off, lights off, disconnect the negative terminal from the battery. Connect one lead of a volt meter (set on DCV) to the negative cable terminal and the other lead to the (-) battery terminal. If you get any reading at all, then you have something drawing current from the battery, could be the security system, the radio's clock, a faulty underhood light mercury switch, a bad brake light switch, etc....You can use a test light instead of a volmeter, but if its a very low current draw the light may not glow...If you have no reading, replace the battery.
  5. COACH

    COACH New Member

    sorry to take so long to get back but anyway...no lights on--not one in glove box...alternator with a bad reg with a leak to ground...how would I check this..going to ground? bad ground...thanks

    - - - Updated - - -

    BCM? Where and what is it? how do u check? thanks

    my truck is an 04 Z71
    Last edited: Jul 30, 2013
  6. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    BCM is the Body Control Module (sometimes called the Truck Control Module), it uses the input from things like headlight switch to turn on the headligts.

    You could have a bad BCM, but don't jump there of the bat.

    Read [MENTION=62013]SilveradoDreamer[/MENTION] post. he is trying to tell you how to find the current drain.

    Connect an amp meter in series with one of the battery leads. If you see a current reading, pull fuses, one at a time (replacing each fuse after you pull it) until you see the current drain fall to zero (or close to zero). That fuse is connected to the circuit that is causing the drain.

    I am afraid, that is the only way to find the problem. you can guess, you can poke around, and you may get lucky; but, far from a good method of testing.
  7. j cat

    j cat Epic Member 5+ Years 1000 Posts


  8. Another Method (borrowed from a friend's blog site)

    1) Remove the negative side battery cable from the negative battery terminal.

    2) Connect the black wire to the com input on the multimeter and the red wire to the 10A or 20A input on the multimeter. the meter needs to be able to read at least a 2 or 3 amps for this test to work. Connecting the red wire to the mA input on the multimeter won't work and could damage the meter.

    3) Attach a multimeter(set the dial on the multimeter to measure Amps as per multimeters instructions) between the negative cable and the negative battery post. Wait a few seconds to several minutes for the car to go into sleep mode - i.e. when you make the contact with the ammeter, the cars computer systems "wake up". After a bit of time they will go back to "sleep".

    4) If the ammeter is reading over 25-50 milliamps, something is using too much battery power.

    5) Go to the fuse panel(s) and remove fuses, one at a time. Pull the main fuses (higher amp ratings)last. Perform the same steps for relays found in the fuse panel. Sometimes relay contacts can fail to release causing a drain. Be sure to observe the ammeter after pulling each fuse or relay.

    6)Watch for the ammeter to drop to acceptable drain. The fuse that reduces the drain is the draw. Consult the owners' manual or service manual to find what circuits are on that fuse.

    7)Check each device (circuit) on that fuse. Stop each lamp, heater, etc. to find the drain.

    8)Repeat steps 1&2 to test your repair. The ammeter will tell you exact numbers.

    9)You can also try unhooking the big wire from your alternator. The alternator can sometimes have a shorted diode that can cause amps to flow through the alternator's power cable and through the shorted diode and into the case and through the bolts and back to the negative battery terminal. This will drain a battery in a hurry.Make sure to read the ammeter before and after unplugging your Alternator.

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