Megohmmeter - Loss of Isolation Diagnostics

Hello I'm Professor John Kelly and this is  the WeberAuto YouTube channel. have you ever   wondered how safe you are from electrical  shock in an electric vehicle if that vehicle   is involved in an accident in this video we  will explore several different scenarios and   show you what happens now a safety warning first  high-voltage systems in electric vehicles can be   very dangerous especially if you are not trained  some of the things I'm going to show you in this   video can be very dangerous if you don't have  the proper tools and the proper training so   please don't try this at home to understand how  safe the high-voltage system is in an electric   vehicle I like to use a flashlight to show my  students how the high-voltage system is insulated   or isolated from the rest of the vehicle so in  this flashlight there are two D cell batteries   so if I take these batteries out each of these  batteries has its own positive terminal and its   own negative terminal we put multiple batteries  together and their voltages add together and in   this flashlight we take two 1.5 volt batteries put  them in series to equal 3 volts now the negative   side of those batteries actually connects to  the metal housing of this flashlight so this   is actually battery negative and you can hold that  all day long and it's not going to hurt you it's   the flashlight won't turn on until I push a button  here to complete the circuit and then we have the   flashlight operating now if I took this flashlight  and just put it in the back seat of your car but   this would pose no danger to you or anyone in your  vehicle the positive terminal this flashlight is   not touching the vehicle chassis the negative  terminal of the flashlight is not touching the   vehicle chassis both of those are electrically  insulated from the rest of the vehicle so the   high-voltage batteries in electric vehicles are  also totally isolated and insulated from the rest   of the vehicle chassis and you as the driver and  your passengers the positive terminal of the high   voltage battery does not touch the vehicle chassis  the negative terminal of the high voltage battery   does not touch the vehicle chassis and electric  vehicle makers have gone to great lengths to make   sure that it's totally isolated just like laying  this flashlight somewhere in your car it's not   going to hurt anything the rest of the car still  runs on the 12 volt system so what happens when a   positive terminal or a negative terminal from the  high-voltage battery does touch the sheet metal   the vehicle chassis well let's take a look  at that so to access the high-voltage battery   positive and battery negative terminals of this  electric vehicle this is a 2017 Chevrolet Bolt EV   underneath the hood is what General Motors  calls the high power distribution module HPDM   but this is nothing more than a junction block we  have a connection right here from the high voltage   battery two cables that come in right here and  then all of these other connections on the sides   are where power is distributed from the battery  to other devices so this distribution block   underneath the hood has a cover that comes off  it has a bunch of bolts going all the way around   the outside that you access from the top it has  two bolts that come in from the bottom that you   can't access from the top and so you cannot take  this off in the vehicle you have to remove this   entire module to take this cover off well I have  purposely removed the screws from the bottom and   put it all back together so that I can take the  cover off and get to the high voltage connections   inside of this box and once again this is very  dangerous this is not something anyone should   do I'm just doing it for a demonstration here so  let's look at the one on the car here and take the   cover off okay as you can see right here under the  hood is the high power distribution module I just   showed you I've already removed all the bolts  I've got my high voltage personal protective   lineman gloves on they're all tested to make sure  that the and I'm just going to lift this cover   off you must wear personal protective equipment  to protect yourself from the high voltage that   could be under this cover if everything is working  right with the vehicle off there is no power under   there and we will verify that here in moment  okay to verify that there's no voltage there or   that there is voltage there force the experiments  I'm going to do I have a fluke 87 series 5 meter   right here and I've got a label on it that reads  isolation voltage so on I've already tested the   meter to make sure it's reading correctly I've  tested the meter Leeds fluke sells a proving   unit that creates a high voltage DC or AC for you  to test your meter your meter leads and so on to   make sure that it's capable of reading those high  voltages so I'm going to take with my insulative   glove on and take the positive terminal from our  volt meter and I'm going to put it right in on   the positive bus bar of this distribution module  and this bus bar is connected right to the front   of the high-voltage battery under the car now  I'm going to take the negative terminal here and   put it right on the bus bar again except this one  is for the negative terminal of the high-voltage   battery and what I want you to see right here  on this meter is that there is no voltage at 1   millivolt point zero zero 1 volts DC now I'm going  to go power up the vehicle and let's watch that   multimeter ok I've just powered up the vehicle  notice that now we are reading 380 1.5 volts   so that is a direct connection to the battery  through the electrical contact or inside the   battery and the contactors are what open when you  shut the car off and close when you turn the car   on to connect battery power to the high voltage  electronics here underneath the hood including the   drive unit to make the vehicle move down the road  okay now I'm going to power off the vehicle and   if everything is working correctly that voltage  should drop right down to close to zero in just a   matter of seconds okay here we go powering off all  right the vehicle is powered off we have 20 volts   18:17 this is the big smoothing or DC coupling  capacitor inside of the inverter that's powering   down it has a parallel resistance with it to draw  that power down so we're down to 10 volts a safe   voltage okay now that we've seen what the normal  voltage is on those terminals let's cause some   malfunctions because at no time should either  the positive or the negative terminal from the   battery be connected to chassis ground which is  the housing of that distribution block well if I   were to come in say with just a jumper wire and  jump either the positive side or the negative   side to the chassis of the vehicle you might  think that that would cause a big problem let's   take a look and see what it does so we're down to  four point seven volts DC so I'm going to connect   the jumper wire right from battery positive the  busbar right to the housing of the distribution   center now I want you to notice that we're still  discharging the capacitor 4.40 one four volts   it made no difference at all having the positive  side of the bus bar connected to vehicle chassis   so let's turn the vehicle on now let's power  on the Chevrolet bolt Evie and see what happens have no warnings no check engine light notice  now that we still have 381.4 volts with   that jumper wire connected now with that jumper  wire connected from high voltage battery positive   to the housing of that distribution module we have  just connected the entire vehicle chassis all the   sheet metal on this vehicle is now connected  to 381.4 volts but that doesn't matter   it's not an unsafe thing because unless you  touch both the high voltage positive and the   high voltage negative at exactly the same time  there's no risk of shock so at this point nothing   has happened that even indicates to the driver of  the vehicle that there is this unwanted connection   to the battery positive so if I open up the  general motors scan tool here the GDS 2 and   I go in and check for diagnostic trouble code  information we'll see if it has triggered any   codes because the computer systems on these cars  monitor for this exact problem this problem is   called loss of isolation on Toyotas they call  it a high voltage leak its loss of isolation   all right it does show that we have triggered some  trouble codes if I click on the code details so on   it has the malfunction indicator lamp request  illuminated so the first code is just to turn   on a warning light the second code says drive  motor one control module hybrid EV battery   voltage system isolation lost and then the other  one says drive motor control module hybrid EV   battery voltage isolation sensing circuit one  low voltage so those three trouble codes are   the ones that we're going to look at I have a few  other trouble codes in here from other things but   we're going to ignore the for this demonstration  so I'm going to power down the vehicle now so what   I just simulated with that yellow jumper wire  was a complete short-circuit from one of your   two high voltage ones battery positive ones  battery negative cables that are that run in   this car and on any electric vehicle I'm using  a Chevrolet bolt but it could be any car I've   just simulated one of these wires being pinched  or rubbed through touching the vehicle chassis   and the car can continue working with one of  those doing that now I can't continue working with   both of them connected to vehicle chassis that  would blow the fuse in the service disconnect   lever under the backseat or some vehicles have the  fuse inside the battery it would definitely blow a   fuse in the car would shut down but you can take  either the positive or the negative cables and   have them completely short-circuited to vehicle  chassis and the car will still operate it'll just   trigger trouble codes those trouble codes are for  loss of isolation and there's a special diagnostic   procedure there's a special multimeter and an  insulation tester or Meg ohm meter as they're   called to go in and measure these high voltage  circuits when they're disconnected and see how   much resistance they have and there's a certain  specification for that resistance alright so   I just short-circuited the positive side to  vehicle chassis let's just change it and do   the negative side and see what happens with that  all right I have high voltage battery negative now   short-circuited to the vehicle chassis let's turn  the vehicle on and see what happens notice our   multimeter is still showing 381.4 volts so  I have just demonstrated that you can completely   short-circuit high-voltage battery positive to  the chassis or high-voltage battery negative to   the chassis and it'll have no effect it triggers  trouble codes I have two more diagnostic trouble   codes on the scan tool for the detection of this  short circuit but the ready light is still on and   the vehicle can still move down the road so in an  automobile accident if either of those two wires   gets pinched to the vehicle chassis it's there's  no danger if both vehicle if both high voltage   wires get pinched to the vehicle chassis at the  same time it should blow the fuse in the battery   or the battery's service disconnect lever and open  circuit the battery to where there's no voltage no   danger there anyway now there are other situations  that can occur that can cause loss of isolation   that is different than a direct short-circuit so  for example if water somehow or coolant leaked   inside the battery or water got inside the battery  or water got inside of any of these high voltage   electronics here the water can be conductive  antifreeze can be conductive the air-conditioning   compressor refrigerant oil can be conductive the  transmission fluid can be conductive under certain   situations and so if the wrong fluids have been  put in the vehicle or if there's a fluid leak   that allows intrusion into these electronics then  we would see a little bit different of a situation   here so the way the vehicle detects unwanted short  circuits in the high voltage battery positive and   high-voltage battery negative is with what is  called active testing and passive testing active   testing is done by the battery which is underneath  the vehicle the computer inside the battery called   the BECM the battery energy control module  performs what is called active testing and   that does that every time you shut the vehicle  off right before it opens both contactors and   disconnects power from this underhood Junction  block it looks to see if there was a loss of   isolation and if there was then it triggers a  trouble code and you will be able to see that   trouble code on the scan tool but that was an  indication of what happened when the vehicle was   shut off that is not an actual live reading if you  were to hook the scan tool up and look like right   now the other type of testing is called passive  testing and it's done by the power inverter module   which is underneath this distribution module and  the power inverter module takes high-voltage DC   power from the battery and converts it to AC power  and to drive the electric motor in the drive unit   the power inverter module performs this passive  testing all the time the vehicle is powered up so   anytime that ready light is on it's watching for  loss of isolation and it's live and we can watch   that on the scan tool so right now I've got the  scan tool powered up and let's take a look at what   happens when we turn on the vehicle with no short  circuits or anything else going on let's just   take a look at the normal reading to begin with  and then we'll begin creating additional short   circuits but through high resistances to simulate  a short circuit through a conductive liquid or   fluid that can happen on these vehicles so we've  got our multimeter disconnected I'm going to power   on the vehicle now okay the vehicle is powered on  and as you can see here the bottom two parameters   our drive motor one control module positive  supply voltage and the bottom one is drive   motor one control module negative supply voltage  and notice that both of those read 190.06   volts at this moment with a total battery pack  voltage in the third from the bottom parameter of   381.06 volts so the way this works is  we take our battery voltage 380 volts we divide   it in two and we have on the positive side through  a resistor network for loss of isolation diagnosis   we draw up half of that voltage so three hundred  and eighty we drop one hundred and ninety of that   across this resistor network to the vehicle  chassis and then that's on the positive side   we do the same thing on the negative side and so  we have all 380 volts dropped across two resistor   networks for Diagnostics on the positive side  and the negative side and we can monitor that   and they tell us in the service information as  long as those two voltages are within 15 volts   of each other then pretty much nothing is wrong  on this vehicle but as the short circuits come   along either a direct short circuit like I showed  you with the jumper wire or through some sort of   a fluid high resistance then those voltages won't  be equal and they will shift and the side with the   loss of isolation its voltage will decrease okay  I'm ready to connect this 10 million ohm resistor   between the high voltage battery positive and  the housing of the Power Distribution box there   but here's here's something to think about I  want to measure the voltage drop across that 10   million ohm resistor as well well the problem is  these fluke 87 meters have an internal impedance   which is measured in ohms of almost 10 million  ohms it's 11 million ohms so the meter itself is   already putting 10 million ohms of resistance in  the circuit so rather than putting this 10 million   ohm resistor in we'll just hook the meter up and  watch where that does to the isolation voltage   differences on the scan tool now the meter on the  left is the one that is you were using to measure   voltage the one on the right we're measuring how  much current goes through this circuit with the 11   million ohms of resistance connected so let's turn  on let's power on the vehicle see what happens all   right the vehicles powered on let's take a look at  what voltage we get so as you can see here we are   measuring 175 point 8 volts from high-voltage  battery positive to the chassis of the vehicle   and notice on the meter on the right that we are  reading seventeen point six micro amps millionths   of an amp so that's an extremely small amount  of current in this circuit and that's what we   would expect with an 11 million ohm resistance  or impedance that this meter is offering so the   voltmeter on the left there showed one hundred  and seventy five point eight volts notice here   on our scan tool that on the positive isolation  side it shows one hundred and seventy-six volts   almost exactly the same thing so that means the  passive isolation testing done by the inverter   module is watching this occur right now all right  so that was with 10 million 11 million ohms of   resistance now let's go to half of that amount  approximately 5 million ohms so next I'm going   to replace the multimeter with its 11 mega ohm  internal impedance with one that's half of that   approximately four point six five mega ohms and  then we'll watch what that does on the scan tool   because now we're cutting the isolation resistance  a little more than in half so it's getting closer   and closer to a direct short-circuit so I'll take  the voltmeter out on the Left we'll just hook up   this short circuit through the amp meter  there and watch how much current goes through it   so let me power down the car first okay I've got  the four point six mega ohm resistor connected in   series with the amp meter short circuiting high  voltage battery positive to the housing let's see   what this does and when we turn on the car okay so  let's take a look at how much current goes through   this four point six five mega ohm resistor and  we get thirty four point six micro amps and if   we look at our scan tool now we get a 160 volt  drop across that resistance rather than the 190   volt drop in a normal situation notice that the  voltage drop on the negative side has gone up and   those two voltages still add together to equal  the 380 volts of the battery itself ok next I'm   going to take out the 4.6 mega ohm resistor and  put in a 1.1 6 mega ohm resistance and see what   that does to our current will shut off the car  first of course okay I've got the 1.1 6 mega   ohm resistance installed let's see what that  does to the voltage drop on the scan tool and   the current through our amp meter here power on  the vehicle ok as you can see here our scan tool   voltage on the positive side has now dropped down  to 109 point nine eight volts and the current has   gone up to 93 point 8 micro amps or ninety three  point eight millionths of an amp ok next we're   going to install a half a million ohm resistance  five hundred and fifty one kilo ohms ok with the   five hundred and fifty 1000 ohm resistor installed  you can see here on the scan tool that the voltage   drop on the positive supply side has dropped  down to 73 point nine seven and the negative   side has gone up to three hundred six point zero  two both sides added together still equal the 380   volts of the battery now we're going to cut that  resistance in half again and we'll go in with a   two hundred and twenty-two thousand ohm resistance  now at some point here there has to be a threshold   where a diagnostic trouble code sets and it does  it sets right around two hundred and sixty four   thousand ohms for the very first failure detected  and then a lot of these trouble codes are a Type   B code meaning they have to have two failures  in a row to turn on the service vehicle soon   light on the second failure I believe it's the  threshold is only three hundred and eighteen   thousand ohms so somewhere between three hundred  and eighteen thousand and two hundred sixty-five   thousand ohms that is the threshold where the car  says alright there's something wrong let's trigger   a code and get this checked out so we're dropping  below that threshold now with the 222 thousand ohm   resistance cycle the power and get that installed  okay we've just powered up the vehicle with two   hundred twenty two thousand ohms of resistance  notice here on the scan tool that the positive   supply voltage isolation voltage is clear down to  forty volts and the negative side has gone up to   three hundred and thirty nine I get an email from  GM's OnStar system saying that there's something   wrong with the high-voltage battery pack whenever  I do this I'm sure they're wondering what is going   on with that car so with two hundred and twenty  two thousand ohms of resistance it looks like   we have one hundred and seventy five point three  micro amps in that same circuit all right our next   resistance will be about half of that one hundred  and seven thousand ohms of resistance okay now   with our one hundred and seven thousand normal  resistor installed our high voltage positive   isolation voltage is dropped down to 20 volts  and the negative has gone up to three hundred   and fifty nine so notice now with a one hundred  and seven thousand ohm resistance we have one   hundred ninety seven point five micro amps of  current so a very small amount of current now   the one measurement I forgot to take is how much  current do we get with zero ohms of resistance so   we've seen everything from the current in eleven  million ohms five million ohms two million ohms 1   million ohms five hundred thousand ohms 222,000  ohms one hundred thousand ohms and now zero so   to create a zero ohm resistance I'll just took the  meter leads together in place of our resistors and   let's power the vehicle back on ok as you can  see here on the scan tool we are down to zero   volts of positive isolation voltage and all three  hundred and seventy nine point nine nine volts   are across the negative supply so a direct short  to chassis ground let's take a look at how much   current we have in this circuit notice that with a  direct short from high-voltage battery positive to   chassis ground we only have two hundred and twenty  two point three micro amps of current so the power   inverter module on this car and there are very  similar systems on everybody else's hybrid and   electric vehicles it monitors these voltage drops  and once it detects a voltage difference between   the high side and the low side of more than a  certain amount or a certain amount of current   depends on the vehicle it triggers a diagnostic  trouble code and will turn on some sort of a   warning message or just show the services vehicle  soon light or check engine light whatever it may   be depending on if it's an all-electric vehicle  or a hybrid electric vehicle but it can detect   these types of problems now why would we have all  of these high resistances that I just mentioned   because in an automobile accident you typically  the circuit might get pinched which is a direct   short like we're looking at right here or the  something might get damaged cracked or whatever   to wear battery coolant or coolant for the power  electronics can get inside of the high-voltage   circuits so what I've got here is just a cup of  water from a bottle of water and we're going to   stick these meter leads into this cup of water  I know it's not a very scientific test but let's   see what just plain water does in this circuit  what type of voltage drop will we get and how   much current will we get let's take a look at  this glass of water now power down the vehicle   so now I've got the circuit being shorted to  chassis through just plain drinking water if   you look right there you can see my glass of  water a couple of meter probes and now let's   power on the vehicle and watch what happens okay  as you can see here on the scan tool it acts just   like a direct short with no resistance we have  a zero volt positive isolation voltage and all   375 volts drop across the negative side so let's  take a look at how much current there is in our   water short circuit here two hundred and sixteen  point nine micro amps almost exactly what it was   with a direct short-circuit so that tells us  that any fluids that are conductive that get   in to the high voltage electronics can cause  a loss of isolation to occur that's why these   batteries that are underneath the vehicles have to  be hermetically sealed there's a smoke test video   that I put together where we test the sealing  integrity of the battery to make sure that no   water can get into it as you drive down wet  slushy wintery your rainy roads even automatic   transmission fluid air conditioning compressor  oil antifreeze any of those things that over time   become more and more conductive can cause a loss  of isolation diagnostic trouble code descent now   how do you determine where this short circuit is  because it's not going to be just right out here   in the open for you to look at if you look at this  Junction block we have an electrical connector for   the air conditioning compressor module so unplug  it and see if the diagnostic trouble code   goes away or if the isolation voltage returns to  normal there's a connection there for the onboard   charger module so when you plug in the external  charge cord to the vehicle just unplug it and see   if the problem goes away there's a heater  for the battery to heat the coolant that goes   into the battery that's another connection here  unplug it see if the problem goes away there's   a passenger compartment heater coolant heater that  has another connection over here you can unplug it   there's a connection on the side here that goes  down to the inverter module if you unplug that   it will isolate the distribution block from the  ability of the inverter module to detect any type   of a problem if the problem goes away then you  know that something in this distribution block   has a problem if the problem is still there then  you know you have a problem inside the inverter   itself the high voltage battery connection  on the back of the distribution block it has to   supply the power to even be monitored so you  can't disconnect that for Diagnostics however   there are two scan tool diagnostic features to  test the battery's internal circuits for loss   of isolation so let's take a look at those let me  disconnect these wires and get everything back to   normal first okay I've disconnected all my short  circuits taking all my wires out of there put the   gasket and the cover back on the distribution  module there and now let's power back up the   vehicle and see if it recovers okay as you can see  here on the scan tool the car has recovered both   isolation voltages are back to 190 volts it has  triggered some diagnostic trouble codes some of   these diagnostic trouble codes you cannot clear  just by undoing the battery or by at or just a   regular scan tool there's a special function to  clear these codes on the scan tool let's take   a look at that next okay as you can see here on  the scan tool screen there's an option to clear   secured high voltage diagnostic trouble codes and  that is a different command than just clearing   diagnostic trouble codes it tells us to turn off  the vehicle open and close the driver door and   then to press Continue on this screen vehicle  off driver door cycled so now I hit continue and we're done okay while we are on this screen if  we come down a couple of items notice that there   is a hybrid EV battery pack active isolation  test so this is the test that is done every time   the vehicle is shut off and the contactors in the  battery open so let's do this test it tells   us to turn the ignition off turn the park lamps on  and then refer to service information for further   instructions and press Continue so ignition is  off I will turn on the park lamps ok the park   lamps are turned on I'm going to hit continue and  notice right up here the top parameter there gives   us the insulation test resistance of two thousand  nine hundred and twenty five kilo ohms which is   two point nine five mega ohms so two point nine  five million ohms of resistance is the isolation   voltage detected inside of the high-voltage  battery by the battery energy control module   to BECM when it shuts down or closes I'm sorry  opens the contactors this is a test that you can't   get in with a mega ohm meter or an insulation  tester and do this test without dropping the   battery down and measuring taking the cover off  and then taking some measurements so this is a   quick easy way to determine if there's a loss  of isolation inside the battery now let's go   back notice now we have a battery pack heater  isolation test now the battery pack heater as   you can see here is underneath the car and it is  controlled over the can Network and so just coming   in with an isolation tester on its electrical  connector doesn't activate it when the heater is   off there it may not show you a loss of isolation  it has to be activated to have that isolation lost   if there's a problem inside the heater itself  so let's run this battery pack heater passive   isolation test it tells us to place the vehicle  in propulsion active mode which is another name   for the ready mode ensure the transmission is in  park and refer to the service manual for further   information or right now the vehicle is off from  our last test so now I have to turn it back on   okay I'll hit continue and then notice that very  top parameter up here has the hybrid EV battery   pack heater power command and right now it's a  0% so the heater is off notice down below here   we have our isolation voltage on the positive and  negative side of about a hundred and ninety volts   apiece which is what we saw before now let's  turn on the heater there's a button down to   the bottom right here so we'll turn it on notice  the percent is going up we're at 45 percent so   we're increasing the amount of power used by the  battery heater I can hear the coolant pump for   the battery heater running and finally we're at  100% so the battery heater is turned on all the   way and notice our isolation voltage is still 100  90 volts apiece and if we scroll down a little bit   it gives us a calculated resistance value of 2900  kilo ohms or 2.9 mega ohms of internal impedance   so notice it says the test has completed and has  passed and so there are two different tests you   can do with the official general motor scan tool  to check for loss of isolation on devices that   are either really hard to get to or you can't  test them unless they're turned on another   example is the air conditioning compressor the  loss of isolation may not occur until the air   conditioning compressor is turned on all right in  the factory service information there are various   tables that show what the resistance should be  as measured with a meter like this one right   here the fluke 1587 insulation tester also known  as a Megohmmeter, I used to think it was megaohm   meter but I looked it up and it's mega ohm meter  which doesn't make sense to me it should be mega   but what do I know any way this meter will use  up to 1000 volts to check resistance so on this   car here we put it we're told to put it on the 500  volt scale and take these resistance measurements   and that way we're simulating the same voltages  that the circuits run on okay if you look closely   at this insulation meter I've turned the rotary  dial all the way over to the far right hand side   as far as I'll go clockwise to the orange labels  50 volts to 1000 volts insulation test then over   here on the two input terminals on the Left we  have insulation and it shows positive on this   red terminal it shows negative on the lower red  terminal we do not use the black common terminal   on the other side so I will take my black meter  lead and plug it into the negative input terminal   on the left and then I could take my red meter  lead and plug it into the top there and take a   resistance measurement by pushing the insulation  test button or there's a different meter lead   that has three input terminals right there and  this meter lead has this button right here to   push to activate the insulation test pushing this  button right here does the same thing as pushing   this button here now on the screen itself notice  that it says we are on the 500 volt scale so that   means this meter can output 500 volts you can also  output a thousand volts so there's a 50 a 100 or   250 of 500 and a 1000 volt scale and you want to  pick a voltage that as that is as high or higher   than the operational voltage of the vehicle so  on the Chevrolet bolt IV here the maximum fully   charged battery voltage is right around 390 volts  so picking the 500-volt scale on this meter is the   one to do and that's what the service information  tells us also but with 500 volts we are going to   need our personal protective equipment on because  this meter as some of my students can attest will   definitely shock you if you don't have your  personal protective equipment on alright now   I have disconnected the air conditioning control  module electrical connector and it has two orange   wires going to it one of the orange wires has a  black stripe that is high-voltage battery negative   the one that's all orange is just high-voltage  battery positive and so the test in the service   information, as you can see here, tells us to check  from high voltage battery positive to chassis   ground so we will run one test two chassis ground  or to the chassis, it's not really ground and then   we'll do another one on the ground side and we are  expecting to see above 550 million ohms which is   what this meter does really well if you tried to  use a regular industrial multimeter to take these   measurements they only can measure between 20 and  40 million ohms at the most dependent on the meter   so let's let me get these meter lee choked up and  we'll run a test I'll put my alligator clip on   connect that to chassis and we'll take our meter  with the probe tip on it and we'll probe each of   the positive and negative wires there so I'm going  to come in and just touch not pierce or probe the   positive side and then push the button and notice  it shows greater than 550 megaohms with 527 volts   applied now let's do the negative side here we go  greater than 550 million ohms with five hundred   and twenty seven volts applied so if there was a  short-circuit from either of these two wires to   the chassis it would have shown up now because if  I put this meter probe on chassis connection and   push the button I get zero megaohms and then if  I have a totally open circuit like right now if I   push the button it gives me the five  hundred and fifty mega ohms as well so it shows   us that we have an open circuit now that is just  the wiring from the distribution block down to the   air conditioning compressor module where it takes  DC converts it to AC and it has its own little   three-phase motor inside the air conditioning  compressor and we can't test that portion of   the circuit but you can you do have the ability  to turn it on and off with the scan tool and do   some testing that way all right well my the main  point I wanted to show you here with this meter is   that you can use it to test using high voltages to  test resistances and the specifications in the GM   the Toyota everybody else to service manual will  give you a minimum resistance that each circuit if   it's in good shape should have and if it's lower  than that then you need to dig in and see what   the problem is okay to wrap up this video I asked  at the start of the video how safe are we with an   electric vehicle if it gets in an accident and  has any of the high voltage circuits pinched to   the chassis or pinched together and I've shown you  what happens or told you what happens on in that   instance we've taken a look at several different  resistance values that simulate different levels   of short circuits to the chassis from the high  voltage systems and I've shown you what a glass of   water does it it's it acts like a direct short and  we've talked about keeping moisture keeping parts   sealed keeping moisture out of things especially  as they age they become more conductive and can   cause loss of oscillations keeping the proper  foods and liquids in your vehicle is important   also all fluids are not the same you need to have  the prescribed exact fluids installed including   your antifreeze your transmission fluid your your  air conditioning compressor oil and so on and   we've seen that we can trigger and clear trouble  codes there are some trouble codes that won't go   away until you have a special scan tool function  to clear them and I've shown you just a little bit   of what the Megohmmeter can do I'm going to have  a separate video on just using the Meg ohm meter   to perform Diagnostics for loss of isolation and  other things so thank you for watching have a good day

Channel: WeberAuto

Views: 140,482

Keywords: WSU, Weber State Automotive, Weber State University, John D. Kelly, Guy in Wheelchair, Professor Kelly, Loss of Isolation, High Voltage Leak, High Voltage Safety, Shock, Electric Vehicles, EV, PHEV, Bolt EV, Volt, LEAF, Tesla, Ford, Mercedes, BMW, Audi, VW, Collision Safety, Diagnostics, Fluke 1587, Insulation Testing, P0AA6, P0AC4, P1E00, P1F17, P1FF4, P302F, P1AF0, P1AF4, P1B0B, P1B41, P1AEC, P1EC6, P1FFF, Voltage Creep, Megohmmeter

Id: 00eEj_EgMas

Length: 46min 11sec (2771 seconds)

Published: Fri Dec 20 2019