Parasitic battery drain-towhaul circuit?

Discussion in 'GM Electrical Tech' started by seamus, Mar 6, 2013.

  1. seamus

    seamus New Member

    Can anyone advise on a battery drain overnight-2002 Chev Silverado 1500 LT
    symptoms: Towhaul button coming on by itself-everything turned off at night-morning-tow haul on-battery drained.

    1) BCM has been reprogrammed at dealer-I replaced the BCM with a used one after first dealer recommended a new BCM because old one was 'sticking'.
    2) Problem of towhaul coming on reappeared after two days of trouble free operation
    3) Checked wiring from shifter switch-orange wire is tow haul circuit wire-will expose column today to check connection again
    4) Tow haul is wired into BCM control so I don't think I can pull its fuse independently

    I suspect grounding problem somewhere in steering column or under dash-a kelsey trailer light and brake control was installed so I cut power to it just as an experiment-BCM is turning on towhaul on its own so I doubt it is the trailer lights circuit but I'm open to any advice.

    Anyone have similar issues? The battery drain was investigated now at one licensed shop and two dealers shops-I have the job now to fix this and its a bit humbling that a dealer spent 6 hours and didn't use a scanner tool immediately-they repeated the licensed shops steps checking charging circuit etc.

    There was a GM service bulletin pointing to BCM reprogramming for 2002 Silverado battery draining symptoms-this has been done.

    Thank you
  2. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    That sounds pretty weird. Logic would say that the BCM in general wouldn't be powered on while the vehicle is off, but I'm sure there's some sort of keep-alive power going to it. It shouldn't be enough to cause the issues you're mentioning though. Hopefully you'll figure it out soon.
  3. bladerunner77

    bladerunner77 New Member

    I had a parasitic drain on my 2003 Suburban. Turned out to be the Radio - a module was not turning off when the vehicle was off. I suggest following:

    - Using a multimeter, you should test each fuse in your vehicle - engine compartment and cab compartment.

    - First, disconnect the negative battery cable and connect your multimeter to the negative battery post and the negative cable (disconnected). Have your multimeter set on milliamps -- you should not see a pull of more than 50 milliamps. If you do, check the fuses.

    - Reconnect the battery then make sure your multimeter is set to milliamps and using both connectors, test each fuse at the top of the fuse (metal tabs). If you see any significant pull above 50 milliamps, that may be the problem.
    *** KEY NOTE HERE: If you're not getting any readings on you multimeter, you may have a short somewhere. You may want to check all you electrical connectors and your PCM.

    - Other things to check - ground connections -- there are several for the engine and other components. Make sure they are not corroded or loose.

    - Check the battery itself. Under normal conditions, it should read between 12 and 13.65 volts - depending on the battery. Check the connections for corrosion and bad connections. I use a battery connector cleaner to clean and remove corrosion.

    - Check your alternator - they are easy to remove - take to any auto parts store like Autozone and they will test it for free.

    I saw the info about the BCM before in my own research, but it was specific to make, model, and year where they were built -- check recall bulletins.

    Good luck!

    p.s. the radio parasitic drain I had was almost 50 AMPS... killed my battery in about 6 hours... and it is brand new.
  4. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    The tow haul circuit is probably a separate issue. It's common for the wiring in the column to break or wear ... or even catch in the shifter linkage and get chewed up -- as the tow haul wires are stupidly small in gauge and poorly positioned in the column. Once they break or wear enough for exposure, they'll ground or get caught in the shifter linkage from time to time -- which will close the circuit and toggle the mode on or off.

    Pay attention to what you are doing that causes tow haul to come on. If it happens when shifting then it's probably worn or broken wires. If it happens when there's body roll (abrupt stopping/starting that causes the nose of the truck to fall or rise ... or hard angling on a curve that rolls the body left/right) then they may be broken and grounding.

    The fix is simple -- open the column, find the orange wires that go up into the shift lever, inspect them, and if worn to exposure then tape them shut and move them to a safe location and secure them (while still allowing for shifter movement). If broken then you can repair them by adding new wire to make the connection, and again securing while allowing for movement.

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