Why Does The Meter Show Incorrect Voltage? 

Back in the 60s, my father in law who was a mechanic in a small town on the east coast of NC had a guy come to his house. He and his family were driving their Volvo from NJ to FL and they were having electrical problems. Others had replaced the battery and alternator. He looked at the car and surmised that the engine wasn't grounded properly and added an additional ground. He refused to charge the guy because he wasn't sure he had fixed the problem. A few days later a large box of FL fruit arrived at his house with a note of gratitude from the NJ family for fixing their car.

Long retired now but 50 years ago I was an electronics tech, and all the experienced guys knew that "if you have a really weird problem that doesn't make any sense, it's a bad ground". I see that this is still true, even in simple electrical circuits.

I've seen this alot on those models over the years. Battery acid leaks straight down on it and rots battery trays away. Good video

You're a good man, Kenny. Take care of your customers without costng more than they can afford.

Held together with duct tape, prayer, and the expertise of Kenny the wrencher! What a winding trail.

Can never have too many grounds, but you sure can have not enough. Grounds are always under engineered. First thing I look for on any vehicle wether it exhibits voltage issue or not. Gotta have + and - to make stuff work. Good catch. Agree with previous post about current flow in your thin gauge wire. The ground that rusted off the battery tray is pretty good size, now just hang out in the air ungrounded and forcing increased current through your wire. Ground wires can never be too big.

From Leo: Good catch on the exact problem. Many German cars had rubber mounted alternators for years. They always had charging issues if you did not install a separate ground. You would have thought that premium brands would not scrimp on a foot of #8 copper wire. That sure sold a lot of alternator rebuilds and towing charges.

Great diagnostics! 👍 “Wait till everybody starts driving their electric cars” - that’s a quote from a last year’s video by Eric at South Main Auto on a corroded ground wire in a GM truck.

I have the same problem with my '84 El Camino! I know what to look for now & fix it right! Once again, I've learned something really useful watching your videos! Thanks!

Lack of ground causes some weird reactions in multi-controller automobiles. Seen that also in my years. Even just a weak battery can cause strange effects. Good video!

I had a used '68 Tempest that started boiling the battery dry and eating alternators. Had it in the dealer serviceman several times with no fix. I finally talked directly to the technician and told him what all was going on and happened to mention at night you could see the headlight dim in conjunction with the turn signals. AH! He said he knew what it was and looked between the engine and the firewall and found a ground strap from the engine to the firewall had been cut by someone. He put a new one on and sent me happily on my way with no further problems.

Really appreciate your style of communication especially with regard to your thought process. We’re really fortunate to have this window to your world- please keep it up and hopefully others will become more aware of you and your channel will blow up! Cheers

I remember chasing this same thing years ago on a dodge pickup. Only way I found it was droplight bulb blew and saw a spark from the throttle linkage. Never forgot that lesson.

I would have replaced the battery tray and reconnected the ground as designed. Great diagnostic and trouble shooting! Love the channel!!!

Many vehicles have multiple ground straps from the engine to the body and frame. They cheaped out on this car putting only one ground strap on, plus out of all places right on the battery tray where corrosion happens?... yeah that'll be sufficient 🙄 To be honest, you should consider putting another ground strap on it, preferably using a battery cable. Don't know if I'd trust that one skinny ground wire you got there, it's really not enough.

Had you connected the two grounds to your multimeter, the voltage drop across the two points would have shown up too.

Keep up the great vids Kenny. Your style is very appealing to guys like myself who ask themselves the same questions when troubleshooting. Yes , at least I do sometimes, talk to myself and ask myself questions, such as you do out loud. Ya can't repair a problem if you don't understand it. The parts cannon sometimes should not even be in the picture, but some use it as a first response. Take care

Good find. Gotta love the old GM and Dodge plastic material they made For the interior and dash, you look at it wrong and it breaks. Real fun to put all that back together after you fix the problem.

I had lost the ground between the motor and firewall which resulted in the ground being just the transmission shifter cable. Under on high load (lights, A/C, Wipers,...) resulted in the plastic in the shifter cable to melt and it would fail to move. Replaced it several times before it got figured out.

I have no idea why you stated you did not have a voltage problem when clearly you did. Voltage is the difference in potential between the negative and positive values. So, if your negative or the positive circuit is corrupt, you have a voltage problem. Thanks for your videos.

This one was biting cars even before computers were in them. Usually the strap between the engine and the body was broken or left out during a rebuild and the ground had to happen via the power train to the back axle and parking brake cable.

Hey Ken, ben/ michigan here. Back in the Sixties multiple taillight cars used to have issues with grounds. If you were behind one at night when the driver hit his brakes some tail lights would go out and others would get bright. We used to call it a "light show.'' Back then the bulbs were drawing a lot more current than today's LEDs and if one or more grounds weren't good enough to handle the power required the legtrizity would seek an alternate route. Today it's not so easy for that scenario to occur due to the extremely low current needed to light an LED. Knowing this though, you can almost always figure that "wierd" light shows and other electrical abnormalities are most likely going to be ground related. A quick visual inspection of the ground connections starting at the battery to engine to body to chassis etc is a big time saver. If nothing obvious turns up, then go after the the other side starting at the battery to PDS and moving away toward the problem area. When you break out the tools, you can see the lack of voltage drop at the various connections, even at the fuses. OK? Have fun with cars. See you later.

I was beginning to suspect a ground problem. I agree with RichardCreel6282 that your new wire is too small. Other than that, good work, Sir.

I actually thought ground when you were explaining things. Ground can cause very weird stuff. I am not sure your ground wire you added is heavy enough. I would put another large wire from battery , or engine, to frame on clean metal.

great to see how you actually Help people who need real help!! you will soon be very Lucky! yesss!

Bad ground was my 1st thought when you said "lost communication, still runs." And with the headlight switch dropping to 7. Good find sir

Really good video Kenny I remember Dan had a similar issue with an ABS module a while ago, he had 12v but could not support a load

Great job. Step back and look hard before jumping in that hole! Another similar culprit is paint after body repairs. Ground connections must be protected before paint or sanded back to metal before reconnecting. Cheers.

Good find . I had one quite a few years ago an auto elec and mechanic had both had a go at . This car ran on lpg and petrol. It died and they couldn’t get power at the fuel pump, or lpg tank . So to make it run they hooked power to the tail light circuit, turn lights on then start car. Turns out there was a burnt out connector in the drivers footwell pillar . Replace the connector and car runs perfectly after that. No more lights on needed to make car run

Great diagnostic thought process. I would have gone down the rabbit hole.. until you showed the bad ground. Honestly easy to miss if your not paying attention. Well done , I wish I lived near your shop.

I love your videos and I have learned a lot. I think people have a tendency to depend on scanners to much. As soon as I started watching this video the first thing that came to mind is bad ground.

Thank you for the video's i cant afford a mechanic so i do the work myself and I'm enjoying working on my vehicle's.

Great video. I always use a dvom and a test light when checking grounds. Especially being up in the salt belt. Also I have used the ground off the powerprobe as well.

Wow amazed one of those cars it still around They were real crap boxes back in the day Inferior felt and sounded like it was falling apart when they were new Knew ground soon as I saw that dome light dim. Just like when you have a really bad ground and try and start it Lights bright hit the starter and everything goes dead for a few seconds

I have a 2003 Ford Focus with a similar issue. I am going to try this to see if it helps. Thanks for the video!

Good job diagnosing the problem, just showing machines/ computers can not tell you what is wrong.

Like how you explain and make me think before you just show the cause and fix. I am more apt to remember these kind of scenarios.

I love these problems. Grounding issues are really strange.

I've ran into the same problem Silverado Great job good advice 👍

I would love to see how a certain speed of the car affected the ground but good fix. In the end, voltage is voltage and whether its a voltage or a ground at fault it means trouble especially for electronics and high current draw items. Thanks so much for making this video.

Good morning Mr Kenny hope y'all have a good day 😁, just as soon as the interior lights dimmed i actually guessed right and thought it was a ground guess I still remember a few things from wiring emergency vehicles lol,by the way Im waiting on more stories sir,i really enjoy them

Thanks for sharing this information about the chevy cavalier, I work on my cousin's car and her dashboard is identical.

That’s a very common problem here in Pennsylvania (rust belt) . Have encountered this a lot, I guessed your problem in the first minute of the video.

Similar thing happened to me. On a 2001 Sebring, could not get the O2 sensor heater monitor to run (OBD II). Tried for weeks. Ran many monitor cycles. It turned out to be the main ground cable from battery to vehicle body. All ground was going thru secondary, smaller diameter wire to the engine and the engine to body ground strap. O2 sensor heater monitor is very sensitivd to voltage. Fixed main cable by re-crimping (cable pulled out of crimp connector - no rust). No parts required and it fixed it. Monitor ran and car passed smog test.

I have seen a lot of these types of problems being fixed by Eric O at SMA & Ivan at Pine Hollow Auto Diagnostics so I would have gone to the ground side of the power set up.Cheers.

Interesting problem. "When is voltage not voltage?" Keep in mind that instruments and gadgets without ground will be seeking ground wherever it can find it. The instruments that do have some ground will be the ground source for others seeking ground. When this happens the component becomes part of the circuit for something else and can become overloaded to the point of burning out, blowing a fuse or likely here, throw a breaker which would reset. It's common for this type of scenario to happen when the ground strap from engine to body is broken. In your situation you should have removed the ground from the broken piece and re-attach it to a bolt on the body because now the body seeks ground through the engine. The ending became part of the circuit. Now you may have alternator or starter problems. Also, you could find arcing from battery to body. That little wire may not stand up to the load when it heats up from extended use like on long trips with blower on high. You might consider re-attaching the battery ground to the body.

This guy was a DJ in a previous life: he likes to hear himself YAK! JC, get the point already!

I've had to do a lot of automotive diagnostics and when I get voltage readings that don't seem to make sense My next step is to put wherever I think my ground is on one lead of the voltmeter and the battery negative on the other and I can't tell you how many times there's been a significant voltage between what I thought was around and what the real ground was and if you don't have a real ground for that meter You're not going to get the kind of data you want how you may misinterpret the data you get but also if the thing you thought was grounded isn't there's probably a problem on the ground side and those are often a lot trickier to find. I had one vehicle where the reverse lights didn't work If a trailer was hooked up. I didn't matter if the trailer was electrically hooked up just put a trailer on the tongue and the reverse lights would fail. It turned out there were two things wrong The first was that the ground to the frame rail up at the front had corroded away ages ago and the second was that one of the bushings for the bed of the pickup truck it failed and now the frame rail was being grounded through the bed of the pickup truck unless you put a trailer on it... This probably wouldn't have been much of an issue but somebody had replaced the pigtails for the reverse lights because the original ones in melted and they had wired the ground for the reverse lights to the frame rail instead of to the original wires, prob. because the wires were old a brittle.

This reminds me of the time (about 40 years ago) when my bro-in-law was installing a CB radio in his truck. It worked in the backyard but when he went down the road it died. Back in the yard it worked again but down the road nothing. We finally figured out he had taken power from the wire that activated the interior dome light. Turned out the radio only had power when the door was open. LOL

Must be it had enough ground to not entirely lose all function! I have seen the ground straps rot off from enginge to chassis,but the huge clue they leave is every single light on the dash illuminates! The ones that have alot of green and corrosion still provide enough to just keep the lights out,but make other tgings very random! Thx for the video .

I bought a plastic welder kit to do some grill repairs on a car and that would definitely work on that dash. That is one busted up dash. It's hot here in Az (118 degrees) but that humidity that you guys have...holy cow.

A dash for that particular year and model can probably be found at a salvage yard somewhere in the area.

Great diagnostic logic as ever. My only concern about your repair is that what potential current will be draw through your new wire. If it’s just the dash electronics it will be fine but a very heavy load/draw could cause issues. But great video as ever. Like button has been hit!

It is a voltage problem!! High resistance in the ground side, creates low voltage on components!!

I had a similar experience with a 1980 ford mustang with the 200 six cylinder and it wouldn't crank,2 mechanics couldn't get it fixed but the local street mechanic looked at it and after 20 minutes he said "the negative cable from the solenoid to the frame had cracked because of road salt,he went to the auto parts store, got a new cable and installed it,reassembled the other cables and put the key in and it started immediately. I called one of the other mechanics and told them what happened, he told me i was lying and hung up- found out later that the mechanic was out of business because of what happened with me along with several other people finding out that he's a part replacer and not a mechanic

Years ago Chrysler K Cars were notorious for tail light malfunctions . I added a ground wire to dozens to fix the issue caused by wet trunks

thanks kenny ! i learned something today 💪🏻

I knew half way thru the video it was a bad ground I always do just a visual of the wiring sometimes it saves you so much time love your channel kenny still wrenching at 73 would a break out box possibly show a bad ground ??

14:05 I had an 09 Yukon , the fan kept kicking on at random and run the battery dead , I changer both relays and the a/c pressure switch. Still not fixed , took it to the dealer , they couldn’t fix it . I went home and cleaned every ground I could find and that fixed it

My 2000 blazer has a tinned braided copper ground strap from the block to the firewall. That ground strap was solid green. I had 2.5 volt voltage drop at the firewall. Things in the car were going goofy. Id get out of the car with the keys in my hand and th heater blower motor would just turn on by itself and couldnt turn it off at the switch. The radio would come on for no reason. Dash light would come on by themselves. A new neg batt cable from batt to block,a length of 6 ga stranded wire from that connection at the block to the firewall problem solved. Made the bcm happy.

Had a Hyundai with an overheating problem. Wasn’t overheating. Ground problem was causing temp gauge to rise when under electrical load, like headlights on.

Powers and grounds are the first thing I inspect for when ghost electrical issues are found

Good info & Excellent troubleshooting !! Why would anyone use a Corrosion prone location like a Lead-Acid battery for any Critical electrical Common connection point ?? ....Just Unbelievable Bad decision from somebody !!

Spot on analysis. Probably from up north. Rust etc.. don’t mean to keep harping on that. Sorry

That was the first thing that came to my mind a ground and I'm not near being a mechanic.

Do the triple ground on all your cars. Avoid the ground issues from day one. Google it. But you run a ground from the engine to battery and to the body and back to the engine.

Excellent example of how important good grounds are.

I would like a set of those Retractable leads .

That's the first thing I thought of part way through your spiel. Dealing with AC power I've seen that too, power present but no results. The return circuit has to be there too. With an open neutral power appears on the hot side but still no proper operation of the circuit ! Should have used a larger gauge wire there though?

Ya I was thinking gm wasn't really using CAN back then so I was kinda doubtful it was a bad module

I had a neighbor come to me because he couldn't get his tractor started, I went to look at it and he had the battery out on a charger, while he was getting the battery to put it back in I checked for continuity from the positive battery terminal through the start switch to the starter solenoid, it all checked out. He put the battery back in and when he tried to start it, nothing. I then checked voltage going through the same circuit and got like 5 volts, but from the positive terminal to the negative terminal it read 12 plus volts. I then checked from the positive terminal to the block and had 5 volts. I told him he had a bad ground. He followed the negative cable back to where it connected to the frame, took it off, cleaned both the cable end and the frame with a wire brush, reconnected it and she started right up.

I have put a ground from engine to body the old cars had a braided ground.

10:35 the cross hanging up means the owner asks for the Lord's blessing to get them to their destination.

While technically it doesn't matter which way current flows, we sometimes don't look at the circuit correctly, while technically knowing better most subliminally regard ground like garbage tip of used electrons. So it can be a good thing to remember that electrons are negative & flow from negative ground to battery positive. ie, the ground is the source of the electricity. So the question becomes, why can't I get enough electrons off the ground source to power all circuits at full load. The answer therefore is, you have a high ground resistance. It seems stupid, but Just looking at it from a different perspective can be very helpful sometimes.

I had a corvette do the same thing had a bad frame ground strap

Wow that thing is going to rot away all it's grounds! Good thing getting it fixed for the customer. I feel for them having to rely on something that rickety.

i got tired of not trusting my meter. i went to tractor supply and got a sprayer power cord 96 inch sku1153839 and a car adapter sku 1028394. about 35 bucks for the pair. i can go in to the power adapter in the dash or clip directly to the battery. even on a pickup i can reach anywhere. there i have a known good ground for my meter and a fused switched power if i need one. i can test any ground point against the battery, or backfeed the power outlet for battery changes. i have a battery feed so i can test that against the circuit i'm testing for voltage drop. its been a cheap lifesaver many times. i had originally made my own up but it just kept coming up missing so this is a good alternative and has never let me down.

Yup I put new cables on first with electrical problems and lots of rust

Kenny...rest assured we always get something from your videos!

Good Diagnosis

It is a voltage problem. The circuit needs to be complete and low resistance, which requires to separate conductive paths.

I worked on a Chevy truck. Did the same thing. Bad ground.

Redundant grounds are MOST important.

Great ideas I have learned so much from these videos

Is that ground wire you added big enough?

Voltage drop pin A of the ALDL connector for fast check of body ground.

Two in one neg cable? And the old side post battery. Double your pleasure, double your fun.

Dumb question! Why would you not run a ground from body metal (you used strut tower) to negative on the battery?

Nice one kenny😊

Don't you have a yearly vehicle government test for roadworthyness of a car ? In the USA ?

I bought a 96 cavalier in 2015 that nobody could figure out why the lights in the dash were on and I ran a ground from the battery to the strut tower and ran that car 3 years with no problem, common problem if you live in the rust belt like I do

On another utube mechanic site, the guy diagnosed a problem caused by someone grounding the battery to the engine instead of the starter and it had magnetized the wheel that the crank sensor was reading. The wheel had to be degaussed to fix the issue.

Easy access if ever the evaporator coil needs replacement.

My '00 Jeep Grand Cherokee is showing below battery voltage on the scanner. Thinking it might be a ground issue.

What the hell are those cables coming out ot the front seats??

I'm down in the Wabbit hole. Trying to find my out !

Just curious,how are you liking your launch scanner

That ground wire to the strut tower is not thick enough ...

bad ground is basic testing , you can not call yourself smart if you find a bad ground

Have the same issues with 2007 Buick Rainer .Strange voltage readings .Replaced temperature control cluster with one from scrap yard ..Lasted 6 months and it died same thing ..Bad Voltage regulators in the cluster short out and got ve you all kinds of error codes .Different issue but same nonsense