How to find a electrical short in modern car

[theKbStockpiler]

I have a family member that has a Chevrolet Cruze with a 5amp short. The problem is that the car only has maybe 10 fuses and 20 modules and a lot of relays.. I can pull fuses/relays out and check for AMP draw but this will only get me down to like a sub system.

So my question is; Will a scanner that checks modules get stored info from the modules or do I have to pull the car all apart and use a clamp on meter to narrow it down?

Thanks in advance!
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[Helfen]

First of all what year? Do you know the Cruze has two fuse boxes. One under the dash, one in the engine compartment.

[TDCTDI]

Is it blowing the fuse or do you have a parasitic circuit that's drawing the battery down after you've shut the car off?
_________________
Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.


GOFUNDYOURSELF, quit asking everyone to do it for you!


An air cooled VW will make you a hoarder.


Do something, anything, to your project every day, and you will eventually complete it.

[theKbStockpiler]

This is how this played out.

The car would behave like it had a short where as it just had enough power to click the solenoid and light up the dash if it sat for over 3 days. The battery would charge up normally and have close to 12.6 after draining the surface charge of not too much.

Cruze's have lots of customer complaints on the net with electrical issues and there is a recall on the negative battery cable for having a lousy crimp on the negative clamp.It would not separate from pulling on it. I cut open the clamp and soldered it onto the cable for good measure. At this point I did not check for a amp draw. I do this amount of work and hope it cures the problem.

The car sits for 3 days and the same thing happens. It does not have enough power to start. The owner wants a new battery and I'm pressed for time so I replace it because there is also complaints that Cruze's have lousy batteries. At this point I get out a clamp on AMP meter and it reads a 3.5 AMP draw.I decide to pull all of the fuses and relays one by one until the draw is found.

I go though all of the fuses/relays and there is still the same draw so I disconnect the fuse-able links one by one and the draw remains.

I figure the meter HAS to be malfunctioning so I put a different meter in series with the negative terminal and there is next to nothing of a draw. I put the clamp on meter back on the negative cable but it reads a little lower. The cable is such that you can only get a clamp on meter in about a 4 inch span of it. As I slide the meter closer to the battery the AMP reading gets higher to 5 AMPs and if I move the clamp on meter the full 4 inches away it significantly drops.

At this point I'm going to assume the battery is defective (4 years old),the second amp meter test was accurate and clamp on meters are not accurate near a battery.

I wanted to add that I like the cruze because it is just big enought that it isn't a sh.t box and it weighs a safe amount of about 3100lbs. They do have a lot of customer complaints though.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[TDCTDI]

It's easier for me to see a light than to try to focus on a multimeter so I solder a piece of wire on either end of an interior light bulb (lower wattage bulbs will burn brighter with less current draw.), remove positive cable from battery & connect one wire from the bulb to the battery terminal & the other to the cable, instant test light. If it's bright, pull each fuse until you can see a difference & trace that circuit from there. VWs will light up the bulb with the courtesy light/comfort module if the door is open, I just close the latch in the door so I can get to the fuses. Be aware of changes in light output as this can mean that you may have multiple parasitic circuits (some will always be there such as clock & module memory.).

If no change in light output when each fuse has been pulled, disconnect power to the end users that aren't fused (Starter & alternator for example) I've had alternators short internally & I also had a rash of vehicles where children fed coins into the CD player only for the coins to settle to the bottom of the unit & ground the circuit board to the case.
_________________
Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.


GOFUNDYOURSELF, quit asking everyone to do it for you!


An air cooled VW will make you a hoarder.


Do something, anything, to your project every day, and you will eventually complete it.

[theKbStockpiler]

The car has a RAP module in it where it shuts eveything off for you after about 15minutes if it's not running and a bunch of Body modules. It has a current sensor on the negative battery cable.The fuel pump will prime after you reconnect the battery sometimes. I switched over to all high impedence meters so If I'm tired I don't fry a semiconductor by accident . I was going to get a noid light but I never got around to it. I did not want to risk buring out my VOM at first because I'm not sure what the amp draw is going to be from how GM has it engineered. My VOM will go to 20AMPs but as the modules are not consistant with what they do when the battery is reconnected I was not eager to put my VOM in series with it.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[TDCTDI]

The bulb isn't going to damage anything & who cares if a 3w or 5w bulb gets blown? It's effectively a fuse. Obviously, the RAP module & the current sensor aren't doing something correctly.
_________________
Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.


GOFUNDYOURSELF, quit asking everyone to do it for you!


An air cooled VW will make you a hoarder.


Do something, anything, to your project every day, and you will eventually complete it.

[theKbStockpiler]

If a meter (bulb) ;that is not high impedance, is put in parallel with the circuit, it will effectively short through the meter (bulb) with as much current that the resistance/impedance will allow.This could be much more current then the circuit is designed for. ECU power supplies are only fused and not the circuits as far as I'm aware.

I should be with it enough to know how I'm loading the circuit at all times but I don't think it's worth the risk. With a high impedance meter there is no risk to the circuit, only the meter.

I assume the RAP is only for devices that the driver can control. A mitchels manual might give a overview of how the newer auto systems work ,or maybe factory training but there is basically nothing on the web about it ,just vague definitions of parts and generalizations on their purpose. The factory manuals I'm aware of with this sort of testing reads like ,"if there is power to pin # 81 and ......' type of thing. No real logic behind it's design.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[KTPhil]

I think I'm getting close to the problem in my Prius...

[TDCTDI]

The way I described it, all you’re doing is using the light bulb as a signal to see if any consumers are drawing power from the battery, you’re not supposed to be trying to attach it to anything like you would with a probe. Disconnect positive cable from clamp, insert bulb between clamp & battery post, that’s it. If there is a current load, the bulb will light up. The wire is just so you can move the bulb to where you can see it while you’re unplugging fuses & relays.
_________________
Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.


GOFUNDYOURSELF, quit asking everyone to do it for you!


An air cooled VW will make you a hoarder.


Do something, anything, to your project every day, and you will eventually complete it.

[theKbStockpiler]

Thanks! I got it.

[nsracing]

Good lord!

If it is blowing fuses - there is a short. If no fuses are blowing why do you say there is a short? If there is a short, you will know it as it will cook something when you put the fresh fuse in there.

If you are looking for some unaccounted voltage draw, then look for that. The usual culprits - compartment lights. If you removed the lightbulbs and you still have draw after you removed all the darn fuses, then obviously something else in there is using draw or voltage.

Make sure you have a functioning battery before you condemn the car. Take it to the shop and do a load-test on it. If the battery checks out then, look at the charging system, make sure that is working properly.

Or maybe it is a bad ground all along or plus side cable. Check the wires.

[VOLKSWAGNUT]

^ yeah.. sounds more like a drain than a short.. Simple terms issue .. me thinks..

Ahh yes battery drains.. one of the worst things to diagnose in the modern auto business..

#1.. Make sure it has the correct reserve capacity battery,,



Use a battery disconnect.. for testing.. it's the only true way to find pesky drains as a full disconnect can sometimes hide the problem..
It's a MUST to maintain electrical connection and integrity after the set up and process starts..
In other words.. the battery must always remain connected albeit through a Ammeter or current testing device.

The ole light light bulb in series test works pretty good on high current drain.. but not so good on low current drain..

The GM procedure for testing is a royal PITA..
Pretty much install a battery disconnect, go drive 20-50 miles activating every freaking thing in the car at least twice..
Bring back and shut off.
I personally have learned to open all doors/hood/trunk (before I main disconnect and start testing) so I can access stuff but ALWAYS being sure to trip the latches shut and /or disable the door open/ajar switches.

Install a recording ammeter (10 amp max is fine) parallel to the disconnect switch, then when the switch is .. un thrown ...(wait 3-5 minutes after engine is off) . it makes the meter now in series and real testing begins. .. (Fluke series 87 (V) )

Wait 30 minutes to start average testing.. 120 minutes to maybe hopefully time out modules.. then test overnight or all day while you work on paying jobs.
If its an average under 30mA for the time period.... its ok..
A recorded spike.. generally wont drain.. hence the average recording meter..

The Onstar module.. is suspect #1 most of the time.. It can get locked on and keep about 400mA drain.. Simply pull the fuses for that module , this leaves the network connections in tact. (Damn that Big Brother)

If its a drain that's 3-4 amps.. its something stuck on or "awake".. Probably a light. Suspect trunk, glove box, visors.. look around... at night.
Another pisser of a fault.. .. is a faulty door latch/ajar switch.. keeping RAP or the BCM awake.. Yeah..a scanner to view door switch parameters is a must but not a definite nail in the head.

Most relay coils will draw 200-350 mA

Feeling around relays and components for heat/warmth can indicate stuck ons too.

High current 3-10 amps are mostly easy to find.. it's those .5-2 ampers that can kick your ass.


Two most recent for me..

The rear window breakage sensor (glass grid) on an XT5 sensor ground was "fuzzy".. kept the BCM awake.... only took about 2 weeks on/off to find it..

Got paid about 2 hours.. oh and .3 diagnosis. :fist:

Another.. a bad RR window switch on an ATS .... not stuck on.. but a simple dtc for the switch that indicated an internal failure.. kept the BCM from going night night.. my testical assistance advisors said no way .... but it fixed the freaking thing nonetheless.
It only got two batteries by a d- tech before it got dumped on me..
Think I may have maybe made one hours pay on that one.... whoo hoo.. but feels more like F U. :fist:

I hate battery drains.. loose my ass on just about every single one of them especially under warranty.
So.. dont bring them to me..

Good luck.. patience prevails .. only if you're a doctor..

.
_________________
aka Ken {o\!/o}
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[qwerty]

I had a problem like this and it took me quite a while to find it - narrowed it down to a fuse that was shared with a lot of accessories and lighting. The problem was the glovebox light was staying on. Of course I couldn't see it until I put my phone on record and shut the glovebox door. Turns out the glovebox door switch wasn't physically contacting and shutting off, so I added a stick on rubber foot to reduce the gap.

[KTPhil]

Check the light in your refrigerator lately?