Tips for a Parasitic Current Draw Test?

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THIS IS NOT A HOW TO ON CURRENT DRAW! I will be doing that video soon. The question came in about needing a ton of special equipment to do a current draw. Here is how I do it.

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Had a fun current draw.2013 Ram 5500 diesel. Work truck for utility company with tool cabinets, beacons, winches, laptops, inverters, crane and more. Had .83 amp draw, would never get lower than that. (using clamp method, which is kinda tricky with 2 batterys. Finally got it to .050 draw. Accessory box for all the circuits in bed would never fully shut off. It took a nice flight across the bay.

SCA

I know it isn't a "how to" but its still helpful. Its always nice to know how someone else does something when it involves automotive troubleshooting.

pospc

I use alligator clip leads with a straight pin clipped on the other end to go down beside the non-testable fuses to hit the contacts.

Nipplator

You hit this perfectly! I've been working in the auto-electric rebuilding industry 10 years, my shop deals with batteries, starters and alternators, and I help customers on a daily basis with parasitic drains and everything you mentioned is 100% correct! i'm going to check out that fuse chart, that's something that I didn't know and I'm sure it will save me some time, Thanks for the info!

Soper

Charles great tip with the fuse and multimeter
the first thing I always have done that alot of people tend to forget is to make sure the top of the battery is clean. if it's dirty especially wet from the battery acid it will have a draw. just connect one of the terminals to your multimeter and the other on the battery and you can see the draw of current from it. so a clean battery top or side if a side post battery is the first thing I do.

braddowns

I've been working on cars since I was 16 and never realized the simplicity of the answer to a very old problem. thanks!

mizzuh

Definitely printing off those charts. Super helpful. I do a ton of parasitic draw tests, but would still be interested to see your video on it. Great video as ever, Charles.

mentaldan

Great tips Charles and the link is awesome! I can use that for sure.

wyattoneable

My suggestion would be to break the connection to the battery and hook the battery with a jumper wire. After 2 hours hook the meter in parallel with the jumper and then disconnect the jumper. This prevents any damage to the meter and does not disturb the circuit.

kennethnichols

Great information, thanks Charles. What do you do when you're trying to check something like a Mk4 or B5 where the fuse panel is on the end of the dash and the door has to be open to get to it?

kellyx

The most bizarre parasitic drain I've encountered was on the early 2000's GM Cavalier/Sunfire platform.

The car passed AVR tests. Starter's good. Alternator's good. Battery is good. Nothing wrong was found. The battery dies every week when not driven. The customer brings the car in to basically get told there's nothing wrong, then they pay for it.

A week later they're back for a warranty claim. Battery is dead again. Rinse repeat. Nothing is mechanically wrong. Five technicians looked at the car and theyre all stumped. We knew the parasitic drain was unusually high at that point, but couldn't locate the source.

It turned out the ECM wasn't turning off when the key was switched off. GM released updated software that required it to be re-flashed at a GM dealership. Very difficult for an average mechanics shop to diagnose.

The customer had to bring it to the dealership and a silly re-flash fixed the problem. Apparently this was a rather widespread problem with those cars.

ElectroVeeDub

A friend with a 2012 Jetta TDI wagon chased this for a while until he found a note somewhere that said if you don't lock the car, some controllers stay alive and slowly drain the battery. He would park he car in the garage, leave it unlocked, and by the end of the weekend the battery would be dead.

dB_

You could use a booster pack as a memory saver, in order to connect your multimeter in series, without disrupting the electrical circuits.

guilhermecolaneri

I work in electronics, and i have a question: A fuse is a short, and a current meter has a resistance to it... So assuming the path of least resistance, surely the meter wouldn't read any current at all?
Also, I've fixed this problem on 3 cars, and all of them had a trunk light that was staying on...Always a good place to look first

martincarey

Are modern DC amp clamps any good? I've been skeptical, since without a changing field (like AC) it's a bit harder to have good accurate measurements. They have to be a bit smarter!

Ariccio