Ot: Fastest way to find a short in trucks electrical system?
Close
Login to Your Account
Page 1 of 5 123 ... LastLast
Results 1 to 20 of 86
  1. #1
    Join Date
    Oct 2010
    Location
    Maryland- USA
    Posts
    3,218
    Post Thanks / Like
    Likes (Given)
    1868
    Likes (Received)
    2083

    Default Ot: Fastest way to find a short in trucks electrical system?

    Ok- wife’s SUV suddenly started running the battery flat when parked.
    I charged it up and pulled the neg- have 12 volts reading on ground back to negative terminal.

    Probably a hot short to chassis but are software shorts possible these days- that is the computer (s) are keeping something hot while car is off?

    Otherwise- fastest way to isolate a short in a modern vehicle?

    Thanks guys

  2. #2
    Join Date
    Oct 2005
    Country
    UNITED STATES
    State/Province
    Pennsylvania
    Posts
    14,273
    Post Thanks / Like

    Default

    That's not a Short, that's a "Parasitic Draw".

    A short would have blown a fuse, or melted a wire.

  3. #3
    Join Date
    Oct 2010
    Location
    Maryland- USA
    Posts
    3,218
    Post Thanks / Like
    Likes (Given)
    1868
    Likes (Received)
    2083

    Default

    Quote Originally Posted by digger doug View Post
    That's not a Short, that's a "Parasitic Draw".

    A short would have blown a fuse, or melted a wire.
    Thanks- my dad always told me:
    “The first thing you should learn about a topic is the vocabulary “...

    But....- a short can live on if the ground is less than the ampacity of the wire/fuse?
    We find it all the time in the marine world where wet and corrosion have created leaks in 12 volt systems- that is my worry here- northern salt zone truck- plenty of corrosion on chassis.
    Or is that still a ‘parasitic draw’ if it hasn’t shorted out?

    Just to find it!
    And the damn software: alarms etc- who knows what the gremlins have decided to worry about in the wee hours..

  4. #4
    Join Date
    Sep 2002
    Location
    People's Republic
    Posts
    2,917
    Post Thanks / Like
    Likes (Given)
    212
    Likes (Received)
    2037

    Default

    you can pull all the fuses, put a current meter between the battery and the cable and replace them one by one and see what causes a current draw

    an alternator that is on its way out can do this and won't have a fuse.

  5. #5
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    25,739
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    8115

    Default

    Quote Originally Posted by Trboatworks View Post
    Thanks- my dad always told me:
    “The first thing you should learn about a topic is the vocabulary “...

    But....- a short can live on if the ground is less than the ampacity of the wire/fuse.
    We find it all the time in the marine world where wet and corrosion have created leaks in 12 volt systems- that is my worry here- northern salt zone truck- plenty of corrosion on chassis.
    Or is that still a ‘parasitic draw’ if it hasn’t shorted out?

    Just to find it!
    And the damn software: alarms etc- who knows what the gremlins have decided to worry about in the wee hours..
    Presuming "blade" fuses, drill one so it is open, solder on leads to put a current meter in series with the gap.

    Swap that rig in for one fuse after another and note the draw for each.

    Now sit down with the schematic and see what those that drew power serve.

    Security 'puters, remote/local door entry module, dashboard clock and such are righteous, but should also be very small draw.

    The rest should send you to physical look-see of a small subset.

    Chassis grounds are worth renewing on general principle, any vehicle ten or more years old, and ESSENTIAL on Aluminium vehicles.

  6. Likes Trboatworks liked this post
  7. #6
    Join Date
    Jul 2009
    Location
    Peoria, IL
    Posts
    11,684
    Post Thanks / Like
    Likes (Given)
    50
    Likes (Received)
    8925

    Default

    On many newer vehicles, various modules power up when the battary in connected. You should put the meter in amp mode and leave it connected for at least 30 minutes before determining you have a draw.

    Don't rule out that you may just have a bad battery.

  8. #7
    Join Date
    Jul 2004
    Location
    central NC
    Posts
    2,560
    Post Thanks / Like
    Likes (Given)
    30
    Likes (Received)
    655

    Default

    I'd be inclined to remove the battery, give it a full charge and then let it sit for 36 hours and measure the voltage. At 12.7 or less, it's getting old, 12.5 or less and it needs to be replaced.

    Steve

  9. Likes Trboatworks, Bobw, Dualkit, Joe Miranda liked this post
  10. #8
    Join Date
    Mar 2005
    Location
    Kansas
    Posts
    7,389
    Post Thanks / Like
    Likes (Given)
    421
    Likes (Received)
    3380

    Default

    Post your vehicle. It may have a module that has a habit of going bad. Heater circuits, courtesy lights, climate control, radio can all have problems.

    Don't pull one fuse at a time. Pull them all, and monitor the draw as you reinsert them. Some may take several minutes for the draw to stop. Some circuits may get power from more than one source.

  11. Likes Trboatworks liked this post
  12. #9
    Join Date
    Oct 2010
    Location
    Maryland- USA
    Posts
    3,218
    Post Thanks / Like
    Likes (Given)
    1868
    Likes (Received)
    2083

    Default

    Brand new battery – I will put a meter on it and leave it for an hour to see what the draw is.
    From full charge the vehicle is pulling down to 12.4 in about ten hours.

    2005 Toyota sequoia

  13. #10
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    25,739
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    8115

    Default

    Quote Originally Posted by ewlsey View Post
    On many newer vehicles, various modules power up when the battary in connected. You should put the meter in amp mode and leave it connected for at least 30 minutes before determining you have a draw.

    Don't rule out that you may just have a bad battery.
    Or a sedentary use pattern.

    It also takes more than 20 minutes of running to replace the consumption an "average" start places on a battery. Far more-yet for a hard start, especially if the running is at night, in rain, where lights and wipers, and/or heater defroster do not leave any surplus, if even they are in balance, low speeds, not in drain already. As they CAN be.

    My "wheels" MUST be placed on maintenance . sustainer chargers and/or/else a visit from a rapid charger about once a month, summers, one a week, winters.

    Trips made most often, "retiree mode" lifestyle are simply too short to even begin to keep even the best of batteries charged.

    And Oh, BTW, I'm overdue for doing the same to the Diesel gen set's series'ed-up 12 Volters, one 12 V charger per-each. Thanks, all!

    The good news? My decent but rather ordinary batteries tend to last easily 50% longer than warranty, sometimes double. Not "luck" Telco pensioner. Modest battery, well-treated can outlast premium battery, roundly abused.

    20CW

  14. Likes steve-l liked this post
  15. #11
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    25,739
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    8115

    Default

    Quote Originally Posted by SteveF View Post
    I'd be inclined to remove the battery, give it a full charge and then let it sit for 36 hours and measure the voltage. At 12.7 or less, it's getting old, 12.5 or less and it needs to be replaced.

    Steve
    Adding a permanent Voltmeter, as the Military found wise over fifty years ago, is cheap and rather GOOD at early-warning. OBDC, the info is IN the system - some modules "need to know".

    Physical voltmeter "in your face" is more realistic than dragging all sorts of poop the 'puters only share when ASKED out of their pointy little-heads with extra gear.

    Which, FWIW, should be WITH the vehicle, if-only the El Cheapo simple one that can reset stuff that can prevent getting safely to a better place to deal with it's complicated ass.

    Only two of the 'puters on a vintage Jaguar determine how WELL it rolls, but two of the other three presume to determine if it is even allowed to roll at all.

    "CAN Bus" is the one they throw the hapless owner under, nothing to do with alleged inter-module arguments, attention bids, and assorted kinkey-fuckery-signalry for Dom / Sub relationships of the moment.

    Over 13 years now, ex-factory, they are a happier and more cooperative band of gypsies if all multi-pin connectors get an annual opening up, dose of contact cleaner, and some exercise before dielectric greasing for the next 12 months peace and quiet - or the hope-of.

    Before I got that shit sorted and added the gear to do it easily? I was actually wondering where TF I could find a Brute Force and Bloody Ignorance Scintilla Vertex magneto and a set of Weber carburettors to just render motation totally independent of complexity!

    Downside? The ODBC rats you out at annual emissions test hookup.

    New age, long since. One must adapt or hire a taxi.

    I'm still good with change.

    Surely is nice to have it always start, first go, cold weather, and be ready to adapt and carry-on, shortly thereafter, regardless of weather or season.

  16. #12
    Join Date
    Oct 2010
    Location
    Maryland- USA
    Posts
    3,218
    Post Thanks / Like
    Likes (Given)
    1868
    Likes (Received)
    2083

    Default

    Cycle depth-
    Yep- this is one table.
    The one I show boat clients from surrette batteries has 6k cycles at 20% discharge and 1.2k cycles at 50%.

    4039e84d-3486-460b-a2e8-96fe0f94cfc8.jpg

    Boats are the worse- undersized house banks perennially under charged- clients toss out $5k worth of batteries after three years of abuse.

  17. #13
    Join Date
    Feb 2005
    Location
    Hatch, NM Chile capital of the WORLD
    Posts
    8,995
    Post Thanks / Like
    Likes (Given)
    13555
    Likes (Received)
    10592

    Default

    Besides the battery itself.. What voltage is it charging at???

  18. #14
    Join Date
    Dec 2008
    Country
    UNITED STATES
    State/Province
    New York
    Posts
    10,021
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    2600

    Default

    i have used DC amp meter. disconnect battery and put amp meter in series. max on amp meter i had was 10 amps DC so truck was off and saw 5 amps being drawn and car key ignition not on, so it should have been zero or very low.
    .
    took fuses out one at a time. for me it was AC fuse. so truck ran with no air conditioning. sometimes those $1000.+ repairs not worth it.
    .
    obviously starting car you pull a lot of amps maybe over 100 amps. i did not have that big a amp meter. i did testing with no key in ignition.

  19. #15
    Join Date
    Sep 2002
    Location
    People's Republic
    Posts
    2,917
    Post Thanks / Like
    Likes (Given)
    212
    Likes (Received)
    2037

    Default

    Oh and any dumb things wrong that would otherwise not be worth investigating? A bad door switch....door locks not working......think of things that are not on the ignition switch

  20. #16
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    25,739
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    8115

    Default

    Quote Originally Posted by Bobw View Post
    Besides the battery itself.. What voltage is it charging at???
    Aye - there's another thing a permanently installed voltmeter gives early-warning on.

    Barely in-float, if even, Goldilocks right, or TOO high from regulator fail. Which - BTW - cooks more batteries and faster than under-charge has ever done.

    Voltmeter even adds the ability to spot a dying or dead cell in the battery when alternator is offline and one sees 8 or 10 volts, not 12.

    Cheap, cheerful, easy to add, need not be pretty-placed, but can be.

  21. #17
    Join Date
    Sep 2011
    Location
    Norfolk England
    Posts
    2,041
    Post Thanks / Like
    Likes (Given)
    2436
    Likes (Received)
    1506

    Default

    Quote Originally Posted by gustafson View Post
    Oh and any dumb things wrong that would otherwise not be worth investigating? A bad door switch....door locks not working......think of things that are not on the ignition switch
    Oh dear,bad door switches. On my Jeep the door switches were non adjustable. I used cycle inner tube repair patches stuck opposite the switches, problem cured.

  22. #18
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    25,739
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    8115

    Default

    Quote Originally Posted by camscan View Post
    Oh dear,bad door switches. On my Jeep the door switches were non adjustable. I used cycle inner tube repair patches stuck opposite the switches, problem cured.
    Door SWITCHES are easy. Door "module" driver's side ONLY, that is master for ingress, egress, seat, wheel, mirrors, and pedal rack position memory, what level of security (eg: cabin motion-sensors on or NOT?) what tomfoolery local or remote wireless key is permitted to do, eg: hold-down opens all glass, sunroof included, but won't CLOSE same unless so programmed for Jaguar/Rover serfs who have neither of kids nor pets, and the cooperation of the landed aristocracy who hold a dealer's staff in thrall?

    BTW - Jaguars are "Feudal system throwbacks" if you did not already know that. What happens when a clever motorbike sidecar sheet metal bender, Billy Lyons is granted a life peerage and becomes "Sir William", responsible for bums-on-seats transport of Royals after Royce and Bentley have gone over to the Jerrican tribes ..

    That door module is one rude, and rudely COSTLY bit player to deal with.

    Beware of vehicles with many doors, but only one keyhole!

  23. #19
    Join Date
    May 2002
    Location
    South Central PA
    Posts
    13,411
    Post Thanks / Like
    Likes (Given)
    2157
    Likes (Received)
    3340

    Default

    FWIW, those cheap HF multimeters have a 10 amp current mode and measure in milliamps, and have a replaceable fuse inside if you exceed 10A. Free with a coupon at times. I find them handy and disposable for diagnoses like this - connect between the battery and ground then plug the fuses in one at a time until the MA jumps up.

    The leads on those usually fail before the meter, if/when you kill a meter save the leads for the next one.

  24. Likes Pathogen liked this post
  25. #20
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    25,739
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    8115

    Default

    Quote Originally Posted by Mud View Post
    FWIW, those cheap HF multimeters have a 10 amp current mode and measure in milliamps, and have a replaceable fuse inside if you exceed 10A. Free with a coupon at times. I find them handy and disposable for diagnoses like this - connect between the battery and ground then plug the fuses in one at a time until the MA jumps up.

    The leads on those usually fail before the meter, if/when you kill a meter save the leads for the next one.
    Automotive is not critical, but if even THINKING about electric motors, DC most of all, same meter, even as a 2d or 3rd one, more better to pitch some of those leads in the dustbin, Day One and sub safer ones, actually.

    It is a MINOR nuisance to prepare a split fuse or just fab a couple of workalike blade probes that can be used by "walking" substitution to measure one specific circuit at a time, minimal fumbling about as to placing the meter or holding leads.

    One has to pull each fuse in any case, yah?

    Putting a meter between the main lead and battery is not as "minor" a nuisance, and is seldom needed.

    More to the point, it is VERY useful to be able to measure that suspect fuse or fuses, several, while still being able to start and run the motor, yah?

    I have never HAD this sort of problem for very long at all. It has never been that hard to isolate - even when much harder to actually FIX - most especially if one studies-up on the problem database for any given vehicle.

    That USED TO mean hanging around the grubby old garages where the tobacco-spitting experts were to be found. Then reading columns in the dead-tree magazines.

    Nowadays, those database are online and easily searched. Damned rare the motor vehicle that is a one-off, rather than same-same with millions of others just like it, so yah - the same s**t does happen over and over again, and it gets ratted-out more than once.

    Find those "probables" and shortlist them from a comfortable seat, save a good deal of UNcomfortable twisting and bending under rude conditions.

    REALLY rare to be "the first one, ever" with a brand-new problem. TONS of guidance out there in motor-vehicle internet-land.

    PM is only incidentally related, if-even that much overlap exists.

    30CW


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •