I utilize a quick, reliable methodology for diagnosing vehicle charging system, starting system and drivability issues. It typically takes just 2 minutes and is based on proving that the ground system is functioning properly on every car or truck before moving on to more extensive diagnosis. I perform this test on almost every car when it comes in… and every car before I finish.

Why start with the ground system? If the ground connections in the engine compartment are bad, you can chase problems across a variety of vehicle systems for hours and still not properly diagnose the root cause. Ensuring proper ground across critical engine connections reduces the potential for confusion. Drivability, you might ask? Yes – if the ground system is not perfect, it can result in multiple DTCs for both the engine and the transmission.

After confirming that the battery is at or near full charge, start the process with a voltage drop test. With the engine running and headlights on, set DVOM to 20 Volts DC, and make the following connections:

  1. Positive (+) battery post to the Negative (–) battery post. Reading should be 14.1 to 14.6V.
  2. Negative (–) battery post to the Engine block. 0.04VDC volts max is expected.
  3. Negative (-) battery post to the body. 0.02VDC max is expected.
  4. Engine block to the Body. 0.02VDC max is expected.

If you get 0.00VDC on tests 2, 3, 4, go back and test with your DVOM set to 2 Volts DC. Only vehicles with a very short negative battery cables will read close to 0.00 volts on the last 3 tests. If you have more than the 0.04VDC or 0.02VDC (respectively) on the last 3 tests, it is time to dig in and clean the ground connections around the engine compartment.

Here’s an example of a bad ground on a 2001 Ford Ranger that was fixed by putting the strap on the correct stud.

What you are measuring is the connection of the various ground cables. As electrons flow from negative to positive, if you don’t have good grounds, you will not have enough electrons to properly power the devices on the circuit.

If the grounds are bad, you may have TOO MANY electrons on something like the engine block, which with components, such as the alternator, to burn out. Why? The alternator puts out current on the negative side into the engine block where it has to go up the negative cable to the battery.

Bad ground on a 2004 Jeep Liberty
Bad ground on a 2004 Jeep Liberty

If you have bad grounds and since some computer sensors and solenoids use the engine ground to supply electrons as half the circuit,  you will just have issues.

I recommend the following additional checks to further confirm proper ground:

  1. Alternator output to the positive (+) battery terminal. Because of the amount of current flowing, it’s going to be more than the 0.04VDC on the negative side, but it’s going to be below 0.10VDC (or very close to it).
  2. Oxygen sensor ground wire to the engine block. This should be 0.02VDC or less.
  3. Oxygen sensor heater ground wire. This should be 0.02VDC or less. If you ever get an oxygen sensor output voltage over 1.0VDC, look for a bad ground on the heater circuit. This usually is found on 3-wire types of oxygen sensor rather than a 4-wire, obd2 O2 sensor.


Wayne P.
Los Angeles, CA

26 thoughts on “Got Good Ground?”

  1. Great article.

    I have an 02 frontier that i believe has bad grounds. Check engine light is on, and i have over ten codes come up. All four o2 sensors, knock sensor, crankshaft sensor…..and aside from the truck occasionally idling a little rough and some minor hesitation with low speed acceleration, it runs good. I pulled my 2000lb boat yesterday with no problems. My question is this…could bad grounds or something in the electrical system be causing this? My exhaust has a small leak, but i still get good flow out of the tailpipe. The shops around here tell me to get exhaust fixed, but he exhuast has been this way for a couple years. Thanks for your time!

    1. The shop’s are correct. Fix the problems you know about first. Fixing an exhaust is very cheap and easy. Those old frontiers are great trucks. I’ve seen ones with over 500k miles on them.

  2. Joe…..I also have a 02 frontier….never had all those codes ….I only have egr reading high…when you have that many sensor codes it is usually bad ground…your exhaust leak will make your truck run rich…o2 sensors only detect air….if you have a scan tool ….look at there reading ..they probably read under the 450 mv threshold..with air leaks in the exhaust you could literally pore gas in the throttle body and the engine will still think it is lean because of the exhaust leak….been smogging cars in calif….find this problem all the time…look at tour plugs…they might be fuel fouled or carboned up……. Good luck….

  3. Hello, I have a grounding issue with my car. The temp gage in my instrument cluster is reading that the car is over heating. My infrared thermal laser gauge says otherwise. The highest temp I got on my car was 222 degrees in the upper radiator hose at hottest spot. I have been told this is still in the normal range.

    I have been told I need a new wiring harness for the behind the dash section! Please, my car is a 2004 Sonata with a V6.

    The temp gauge shows in red with load on ground. For example the gauge rises quickly when AC on max and highest speed. It also will rise with headlights on only but at a much slower pace. At first I thought it was just when the AC was on but I had windows down and lights on the other day and noticed the gauge was running hot, however I don’t believe it was in the red. But still over the half line which this car when new and until recently always ran below the half line for the temp gauge in cluster.

    I ran a 12 gauge CU stranded wire from the negative battery post to the engine block. And also ran the 12 gauge wire from the engine to firewall, actually put on same place as existing wire. What I didn’t do is run another wire from the negative battery post to the chassis. However, I thought I had the gauge issue fixed until third test drive which I really ran it good. I ran car for a 45 min drive with AC on max entire time but not necessarily on high blower speed, actually too cold and turned it to low speed yet still on max and recirculate. I also sat for 30 minutes with AC on max and low speed while doing some work in parking lot on computer, then drove 45 minutes back home. Thought I was successful with gauge but last 5 minutes the gauge went a little over half and I was getting nervous, it even seemed that while at a stop just prior to ending the trip the car ran a odd, sort of a miss I guess. Car runs smooth normally. I then checked temp of upper radiator hose and that is when I got the 222 degrees. The other test drives 211 degrees was max and gauge was below the half line where it is supposed to be. After several hours took for a 10 min drive and temp gauge was where I like to see it.

    I believe I still need to add a ground from the battery negative post to chassis and perhaps maybe a larger gauge wire. This car doesn’t use braided ground straps and they seem small from the factory to begin with. Yet for years they did work. I haven’t changed the spark plug wires yet, perhaps arcing? Car is 10 years old with less than 90K.

    Could really use some help. Dealer had car for over a week, not that they worked on it all that time, but after several parts, determined ground and then decided that a wiring harness would be next!

    I believe it to be a ground issue and as stated above.

    Thanks for consideration.

    1. Dean,
      Wow! Sounds like a tricky situation. I am not sure we’re your best resource for suggestions, but we have posted your comment so that the professional technicians among our audience can review it and perhaps provide suggestions. Good luck!
      Jim O’Hara
      Clore Automotive

  4. dean i am the person who assembled the 4 part test. its actually six parts now.. i just found this post. and its been a few months since you posted..

    you should have a radiator fan relay.. and a condenser fan relay… i don’t see a lot of sonatas .. so i am unfamilar with the underhood..

    do you have one cooling fan or two.. does the second fan come on when you have the AC running..

    you might want to carefully examine the radiator fan relay circuits and the condenser fan relay circuits to make sure the relays actually do power up the various fans properly..

    best of luck..

  5. six parts of the voltage drop test…

    after verifying battery voltage is over 12.5 volts..

    engine running headlights on.. DVOM set to 20 volts DC.

    ONE. Negative battery post to the Positive battery post. 14.1 to 14.8 volts.

    TWO. Negative battery post to the engine block. 0.04 volts DC max.

    THREE. Negative battery post to the Body. 0.02 volts DC max.

    FOUR. Engine block to the Body.. 0.02 volts DC max..

    FIVE. Positive battery post to multiple fuses in the underhood fuse block. 0.04 volts DC max in many cases..

    SIX. Positive battery post to the alternator output STUD.. this can be 0.3 volts on some cars depending on the length of the charging circuit.. less is better.. old mopars with amp meters in the dashboard.. expect 0.7 volts. because of the length of the circuit..

    why test 5 and 6…

    98 C2500.. kept blowing alternators

    on test 4 i found 8.5 volts.. cleaned the ground connections at the bottom front of the block.. cured that.. on test 5.. i found around 3.2 volts.. the power connections between the battery and the underhood fuse block were dirty and actually had a frayed wire inside the insulation.. test 6.. was over 2 volts.. the last person who installed the alternator did not fully tighten the nut on the alternator output.. which is why i measure from the STUD not the ring terminal..

    that truck ran great for another 10K miles or so.. till the owner ran it out of oil..

    98 S10.. this truck had always had electrical issues… 1 thru 4 were ok.. test 5 when i was testing various fuses in the fuse box.. some were right at 0.04.. some were up around 2 volts. what.. i looked carefully.. there is a stud sticking up on the corner of the underhood fuse block nearest the master cylinder.. there is a brass strip over that stud base.. but NO NUT.. i picked up a 6MM nut and installed it.. cured that trucks gremlins.. that is not the only 98 s10 that is missing that nut.. i have talked to people about it and found 2 others.. seems that brass strip feeds part of the fuse box..

    2005 chrysler minivan.. when the power sliding door is used. the entire lighting system goes crazy.. super bright and them dim.. super bright and dim.. flashing actually is how its described..

    the dealer techs quoted the owner almost 2 grand in repairs.. alternator, battery, under hood fuse box/IPM, perhaps the wiring harness also.. i had the owner run the six parts of the test.. test 1 was bouncing all over when the lights were surging.. test 2, 3 and 4 were bouncing slightly.. test 5 and 6 were going so crazy it could not be read properly.. i had him narrow the test location points.. on test 5.. when he got to the Positive battery terminal clamp to the strands of wire into the crimp terminal. that’s were it was.. a loose factory crimp on the positive cable.. he wiggled the wires and they were actually loose.. he used a deka replacement pigtail end to replace it..

    the alternator output is connected to the starter stud then up to the positive battery post.. the other wire off the battery positive post feeds the underhood fuse block IPM.. when the power door actuator is used.. the current exceeds the loose connection ability.. this drops the current/voltage to the IPM .. that powers the PCM so the PCM sees reduced power and ramps up the alternator output.. the alternator comes up a second later sending out excessive voltage.. but the loose connection is still an issue. the IPM and PCM see the crazy high voltage now and the PCM shuts off the alternator.. a second later the voltage drops again and the pcm commands the alternator on again.. delay feed back error.. found in just a few minutes with voltage drop testing.. cost to fix.. just a few bucks.. lost sales in parts.. yes.. but how can you charge for items that did not fix the issue.. did you just make a customer forever.. probably.. they will think you are a magician..

    wayne… fixer of the unfixable.

  6. Good stuff Wayne.

    Help! I have a 2006 Ford F350 – 6.0L. The truck has had electrical issues since I bought it. Not too long ago I cranked and began to idle very rough, giving me multiple DTCs involving glow plug circuits. Then I noticed that when it ran rough, the odometer reading on digital gauge disappeared. I could reach under the dash and sorta twist the fuse box and when I held my mouth just right the odometer reading would appear and the truck would start running right immediately. Then I may be going down the road and odometer gauge go blank and truck go dead. It would take a while to restart, but if I got it started and got the odometer reading to appear everything would be fine again. This went on for a while until recently when “this thing” started happening but I could no longer maneuver under dash fuse box in such a way to make it stop. Again, odometer is not showing….now…unless I have the driver door open. While door is open, odometer shows, but truck still runs rough. Im a novice mechanic to say the least and Im at a complete loss, so any suggestions would be greatly appreciated.

    will testing ground to fuses on interior fuse box help me find source? Truck running? As I said, any direction at this point would be great.


    1. Dustin,

      Sure sounds like you have wiring issues, but whether it is related to a faulty connection, a bad fuse or a poor ground would be hard to determine. We would suggest checking for related DTCs in the vehicle information, checking all wiring connections to the fuse box in questions (with an accurate schematic for reference) and checking for any TSBs related to this issue for this vehicle. Beyond that, perhaps you could post your issue to iATN or another technician’s forum. We hope this helps. Clore Automotive

  7. Appreciate this post. My son has a 1989 Toyota pickup with the inevitable electrical issues that come with a 30 year old truck. Initial measurements on the first 4:
    1-neg post to pos post 13.57
    2-neg post to block.014
    3-neg post to body.055
    4-block to body.06
    6-pos post to alt stud.568

    I cleaned up the grounds from the battery neg post to the body (10 gauge wire) and from the body to the block by sanding off paint at these connections and readings improved marginally to.041 for test 3 and .052 for test 4.

    Then I started looking around for a ground between the block and the frame and couldn’t locate one anywhere, so I added one using 10 gauge wire (to be replaced with a ground strap) and now am getting the following readings:

    1-neg post to pos post 13.73
    2-neg post to block.011
    3-neg post to body.000
    4-block to body.011
    6-pos post to alt stud-not measured

    I don’t know what benefits we’ll see from this but he’s got a big subwoofer in the truck and having better grounds can’t hurt.

    Thanks again for the post.

    1. Steve – Thanks for adding to the discussion. For sure, accounting for and improving your vehicle grounds will help, especially when adding aftermarket equipment such as the subwoofer. Good luck with this one. Jim from Clore Automotive

  8. I have a 2001 Ford Explorer sport trac. I went through a car wash last night and when I got out of car wash my ac wasn’t working. Ac compressor isn’t kicking on and off. So I got under truck to see if I could find anything that could have come unplugged or broke off. Week in doing that I noticed that both grounds on passenger and driver side is corroded in half. I am wondering if this could be why my ac compressor is not coming on thus causing my acto not cool

    1. Damon – Thanks for adding to the discussion. It sure sound like a ground issue could be the root of your problem. We would address it as the first step in possibly resolving your issue. Thanks again, Jim from Clore Automotive

  9. the best ” grounding point” is the battery. everybody i know that fiddels with electronics in cars uses + and minus on the battery.
    especially the ones who is building car stereo etc.
    also they are using exta grounding points in the car chassie.
    i for my selv have 4 x batteries in my car in parallell.
    + + and minus to minus etc. 270 ampere alternator, and 50mm2 cabels.
    nave no problems with blinking lights, low voltage, or anything similar.
    so use the – on the battery for ground.. it is also the cleanest point.
    IF you can also ground it in the chassie, BUT then the flow goes through every singel ” grounding point in your car ..
    if you use your battery, it goes right where it is supposed to.
    anywas. thick cables. a good alternator and whole , good and efficient batteries .. that is <3

  10. btw.. i don`t mean to sound like a ” Efin know it all.
    what i know, i do know well, but i am still eager to learn more.
    and when it comes to ” grounding” , i use minus on the battery because of the curent.
    many people say that it is wrong to use the nagative side on the battery as grounding, but it is not.
    take this as an example. let us say that you have a 1993 volvo 850.
    in that car, ( and cars from that era), there are a lot of welding, and welding points. if you ground your battery in the chassie, the current will go through every point in your car . grounding also takes the shortest way.
    if you use the ground from your battery, the current goes from one point to another.. . that ias also the shortest way.
    BUT if you are going to ground in the chassie of the car, make sure that the contact is 100 % good

    also yeah.. i have enough power ^^.
    that is pretty importaint as we are moving over from autum to winter -.-

  11. also i can add that normally, the voltage in a car is everything from 13.7 -14.4 or 14.8. that depends on how ” big” alternator and battery you have.
    also normally, in regular cars you find alternators from 90-180AH.
    at least that is how it is here in norway. i Don`t know if you are working with cars ar or ehat not, but i just felt the urge to give som extra info about grounding. batteries and car electronics. the more you know 🙂
    back to the point. i also would like to add that if people are asking for a extra batttery in their car, make sure that it is the same size as the one that is in there .
    2 equally good batteries is good for the car.
    take this as an example. if the batery that`s sits in the car is a 100 ampere, and the extra you want to put in is a 90 ampere, the ” strongest” of the two will be as weak as the weakest.
    the 100 amp battery will lose 5 amps because of the 95ah battery,
    Also if people tells you that they wanna wire them in series, JUST SAY A BIG FAT NO.
    cars = 12 volt. wiring them in series will give 24 volts.
    so parallell wiring is the clue there.
    also like i wrote in my previous comment, as the season change from autum to winter, a little bit of extra power is good.
    there is one more thing i like to add. or maybe two.
    1. capaciators. NO.. just no.. if people ask you about capacitators, they are really to no big use. the also needs to be charged up. they are also there so you have that little ” extra” to give when you listen to songs with a lot of bass. it will ” prevent” blinking lights, and low volt drops. the solution here is to have enough power and good grounding..
    2. back to the grounding part.
    blinking in lights can occure even if you don`t have a stereo in your car.. if either your generator is weak, or your batttery is weak, lightis will dim and get less efficent if you have your car fan and heaters on.
    heaters , seat warmers and and the car fan is the things the steals the most power.
    the easy solution here is put a extra grounding cable from your battery to the chassie on the car. just make sure that the connection is good, and that that there is a good current flow 🙂

    sorry for my not so very good english.. i have a little case of dyslexia..
    i still hope that you understand what i write.. 🙂

    1. Railgun – Thanks for adding to the discussion. You make some great points. We agree wholeheartedly that anytime you pair two batteries, they should be the same size and condition. As you point out, mismatched pairs will result in degradation to one of the batteries in the pair. We really appreciate your comments and your English seems pretty darn good to us. Thanks again, Jim from Clore Automotive

  12. I have a 2000 S10 4×4 Extended Cab LS and I’m having an issue where power to the cab comes and goes. All the gauges shut off, engine temp gauge slowly goes all the way up, radio shuts off, cabin and dash lights don’t work, headlights don’t work except the brights but I have to hold the switch, power windows and locks don’t work, etc. when it happens there’s a clicking like sound coming from inside the dash. Any suggestions on what that may be?

    1. Cyle – Honestly, we aren’t technicians, so we are not really qualified to diagnose this issue, but many of our readers are. Perhaps another poster would have a theory on this one and make a suggestion on what to check. Thanks, Jim from Clore Automotive

      1. Hey Jim,
        I appreciate the response, I understand that, I was just looking for a place to start. I’ve checked the fuses and had the alternator tested already and I just wasn’t sure what else to look for. I was told possibly the BCM but again just looking for a bit of guidance. Again I truly appreciate the response!

  13. Would a poor ground melt the fuel relay? 2006 Cadillac Escalade fuel relay gets hot and melts? The shop I took it to today said thats just what happens when relay gets old. It has been happening for a while and been swapping ac relay when it shuts down and it has melted that one too.

    1. Alice – thanks for joining the discussion. We would suspect that there is a root cause that is causing this to happen over and over again. Your best bet would be to take your vehicle in for a diagnostic service. The source of the problem could be a poor ground or other electrical problem. But, finding the root cause is the best course of action. Thanks, Jim from Clore Automotive

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