Another Lesson In Voltage Drop - Don't Skip The Basics!

Seems like we cover this all the time, but it is a very essential test for any component that you are testing. This is not just for starters and alternators. Hope this video helps you in your diagnostic thought process.
-Enjoy!

Thank you so much for the support!
--Eric & Vanessa O.

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[TStheDeplorable]

An old man's car died in the McDonald's drive-through. After pushing him out of the lane I figured out that it was getting no fuel. I diagnosed a dead fuel pump, and he said that was his third dead fuel pump in 18 months. But I also noticed on the computer that the car was showing only 10 volts when running. I replaced the fuel pump and his car ran again, but I also knew that the low voltage could be the reason the fuel pumps were dying. The very first thing I checked for voltage drop was from the battery post to the battery clamp, and there were my 4 volts, basically two volts per post. I removed the clamps and found both posts coated with something like varnish. I cleaned them and boom, 14 volts when the engine was running. Hopefully that will keep the new fuel pump from burning out fast like the previous ones. By the way, I'm a DIYer who learned voltage drop testing on this channel (along with most of everything else I know about cars).

[adrenna]

Retired electrical engineer. Your explanation is spot on. Ohms law says it takes 1 volt to push 1 amp through 1 ohm. Every connection, piece of wire and anything else between two points is potential resistance. The rusty terminal caused the extra resistance in this circuit. The conservation of energy law says that energy cannot be destroyed, just transferred. With resistance, its's transferred to heat. As the temperature on that rusty terminal was raised, the resistance got worse and made the voltage drop worse until the point where there wasn't enough voltage to start the car. We saw this on the Honda battery terminal in your last video when you "let the smoke out". Again, spot on, perfectly explained and easily When your body gives out from working on cars, you should

[beefeekeefee]

Can't believe whoever went through the hassle to change that battery didn't take 2 minutes to clean visible rust/ corrosion off the clamp and cable. Also can't believe anybody else does a better job of explaining electrical diagnosis and trouble shooting than you do. Thanks and keep it up!

[danimal]

This is exactly why my headlights were flickering on my 2011 Silverado. Bad negative terminal at the battery. After a round of YouTube voltage drop lessons, I narrowed it down and replaced the terminal end. Fixed the problem, and gave myself confidence that “If you can do it, I can do it.”

[booterone]

Eric has a better understanding of electrical diagnosis than many electricians I have worked with.

[clintprice]

You always are methodical and use logic which is why we are all here, to see a master at his craft.

[ChrisVargasrphtchris]

Saturday with Mr. O is better than Saturday cartoons. You can learn so much from this YouTube Channel.

[timothyoneill]

I repair radiation treatment systems for a living and this is a very good refresher for anyone. You did an outstanding job on this.

[vilefly]

One the days when I am feeling old, I point the FLIR camera at it after cranking the engine, and look for the hot spots. The voltage drop check is still more accurate and cheaper, though. I bought the silly thing to test cooling systems and catalytic converters, but ended up using it for electrical faults. Hotspot in a fuse box? Boom. Found it. At least it wasn't a total waste of money.

[reasongether]

The video makes perfect sense, but the fact that they had the battery replaced to attempt to fix this problem without cleaning the terminals is crazy! Great job once again Eric!

[dgk]

I really like this channel. 1 - you cover the essentials of being a mechanic in the rust belt. 2 - you cover what is involved in diagnosing and fixing modern cars. As you said once, it is all about the data. Thankyou Mr O and Mrs O.

[PhillipBailey]

Great demonstration! I typically teach a maximum of 0.1v per connection and 0.1v for every meter of battery cable. Never to exceed 0.5v for the entire insulated circuit or entire ground circuit..This only applies to high current circuits such as starter and alternator testing. I'll bet on that car if you cranked it for 15 seconds in clear flood mode you would be able to "see" a hot connection with a thermal camera. 1volt times 100amps is 100watts. That's got to warm up something...

[donniev]

Gotta love Dodge aka Stellantis for putting the battery in such a remarkably accessible position, aye? Thanks for the educational video, Eric!

[Motronic]

I think that junkyard paint on the light is telling a story. Perhaps one like that's how the body shop put it back together after it got hit in the front end.

[donaldhollums]

It’s always fun to watch a pro at work.

[jeffreyweinzierl]

I learned voltage drop when I was in trade school. That was a long time ago. (1984), Over the past 40 years I've only had a handful of times when it would have come in handy, but of course, for the most part I worked at new car dealerships. I'm semi retired now and I work on old rusty junk. These refresher courses on voltage drop will come in handy. Thank you.

[garyisaac]

Eric gets us to the answers by the shortest possible route. Love it!

[smc]

I learned the hard way too that checking every connection point also applies when checking for opens/shorts. I couldn't figure out why one of my TPS on the throttle body was showing 0v but everywhere in the circuit was 5v. Then by accident I pressed really hard on the connecter and the voltage came back, some how there was a failure from the back of the wire in the connector to the front of the pin, lol. I checked the voltage everywhere except the place it mattered, lol.

[CedroCron]

So easy but people get it so wrong... I will never understand! But I guess that is what really sets shops like yours apart. "Knowing your craft".

[hughkoontz]

As a 26 year veteran science teacher, that was one of the best most concise explainations of voltage drop I've seen! Great job Eric