No Start from a shorted MAP sensor (Honda, Acura)

okay guys we got a real good one here today this is a 2005 Honda Element with a 2.4 liter engine history with the vehicle this was brought in to the school for an engine replacement and our engine class replaced the engine and it is now a no start I was told that it did run when it came in and with this engine swap we now have a no start situation let me take a moment to talk about direction here and where you start I think one of the difficult things as I continue to film these different case studies is where to take you where to start and I don't think there really is one right way to do this we can go scan tool first we can look for codes we could right away look for spark the coils are easily accessible we could look at fuel pressure there's a lot of different directions that we can take so again just want to emphasize that my approach is probably different for every car I work on it just depends on the car the symptoms the situation and what components are accessible in which are not as far as direction and where to start so I think for you guys for this video I'm going to take you to the scan tool first and we're going to see if we can communicate with it and get trouble codes out of it ok so I already have my vehicle identified 2005 Honda Element I'm going to select engine and I have the right adapter and chip already installed and where to go codes hoping for some guidance here with a trouble code you know maybe things were left on plugs who knows and what we find is we have a no communication with the engine computer so definitely something could have been left unplugged maybe a main power or main ground in particular the grounds remember the engine was was swapped out let's see if this data link connector is actually functional and we'll try talking to a different module what I found when we have no communication problems typically what I do is I will check pin 16 for a power and what you'll find most of the time at least here at the school what I find is that either a a student has misidentified the vehicle or B we have no power on pin 16 so this is one of the ways that we can address that is to see if it talks to other modules so we'll go to the transmission see if we can talk to the TCM same thing looking for trouble codes and I've no communication there too so I'm going to exit go back to our ABS and you see we have some ABS code so what that tells me is most likely pin 16 has power and we're talking on this network so I'm not concerned about a datalink problem in this case or a misidentified vehicle I am definitely worried about engine and transmission and why these aren't talking to us so we're going to move now away from the scan tool and away from the data link connector and we're going to go toward main powers and grounds at this engine computer remember this thing just had an engine replaced so of course the grounds are a big concern here all right I've brought you inside the car before we do computer powers and ground testing there's a few other things we can do one is to take note of our check engine light see if it's lit and it is turn key off key back on our check engine light is lit we do have an anti-theft light or key light that's blinking on and off so we'll take note of that too could be an anti-theft problem I'm going to crank it so you can hear it so you hear it is a no start we're not sure what we're missing yet we haven't checked any of that I'm concerned about a no communication issue though combined with a no start that's a big time problem so before we do powers and grounds I'm going to give you one more check under the hood that's easy to do and that is to check the five volt reference circuit so we're going to go back under the hood all right before I do this reference test I want to talk about when I want to do this you know sometimes we can have vehicles that come in with a no communication problem and it has nothing to do with the engine performance issue you know we can have a blown fuse to the data link connector and we have no communication with the scan tool in the car still runs so the same thing with a nose start is our nose start tied in with the no communication problem or not and I think this test addresses that check for a five volt reference on one of the sensors and what that does is tells you whether or not a computer is alive and talking to you so I generally choose the TPS because it's an easy location to do a test and I'll get you a shot of where I'm connected so I have you zoomed in on one of the TPS right now kind of a shot through this area in front of the grill you can kind of see where I'm connected and I don't have a wiring diagram yet you don't need one if you know these fundamental principles of how a potentiometer works we know that one of the three wires on this three wire potentiometer is going to have five volts on it so that's universal across the board on any year make a model car although there are some variables on some of the older cars that you switch inputs for the throttle that is not the case on this car so what I'm going to do is just move the T pin down the line and take measurements on all three wires so I'll take a measurement on this one and then I'll move it down to the next two in succession and what I will do is have you focused up on the scope while I'm doing that and we'll see the result of this test okay I'm set up on a two second screen 10 volt scale just personal preference I'll get your reading on this first wire and this would be well wire color really doesn't matter we don't have a diagram so point zero to potentially a sensor ground move to the next wire again we're just looking for five volts here we're not really worried about the TPS signal we are worried about our five volt reference and really our ground looked like we had a good sensor ground there's a reading of 1.5 volts on that wire that looks a little high for a signal wire at idle and we'll go to the next pin and we're reading one point seven volts so here's what we know right away with where we are with this vehicle we have a five volt reference circuit problem the computer should be sending five on one of these three wires and it's not so again I didn't know exactly which one was the five volt reference wire but I know for sure that one of them should be five and we don't have that so here's here's the direction change up now if you were doing an O start you check for spark check for fuel check for compression and all of that stuff where we are right now we don't need to do I'm not going to bother checking for spark I'm not going to bother checking for injection pulse or fuel pressure or compression for that matter I need to fix this five volt reference circuit this is a main life line for this computer system if this reference circuit is sorted it's going to pull everything down including a communication issue with the scan tool now most of the time it would also kill the check engine light if that was the case but not always so I think before we would pull a diagram and find out all the sensors that share this five volt reference I think the next step would be powers and grounds because that's the most common issue you have low voltage or no reference voltage generally what you have is a power or ground problem on that sister but we definitely have a reference circuit issue we're on the right path powers and grounds are coming next and again I'm looking to shortcut this and what I've done so far is pull the diagram mark them up and I'll show you that in a second but my main concern in this diagram was to show you guys the computer grounds let me get you a shot on the block here where these computer grounds are they're right here in this location and according to the wiring diagram there are four main grounds that are coming from the engine computer and those colors right there match my diagram so we can actually do a ground check right there and I've shown this before the last vehicle that we had I think it was a toyota echo that had an issue and I think that vehicle ran but it had bad computer grounds if you guys remember from that video and it had to do with a salvage yard engine that this aluminum housing oxidizes and then you bolt the eyelet onto an oxidized housing and you have a bad ground so can we quickly identify this ground connection without taking the bolt off and cleaning it up the answer is yes it's very simple just take your lead you were using for your previous test and connect it to the eyelet not on the housing but I'm back away from the housing away from the boat and get a voltage reading right there if this ground is bad this voltage right here will be elevated so I am connected to that right now the key is still on and let me get you a shot on the scope and I basically have zero volts on that location so that is not a bad ground or suspicions of the engine being replaced and somebody leaving a ground off or probably not the case I could sort cut this for you guys but I think it's important to do the process and the process next is going to be go to the computer and check your powers and grounds directly at the computer well that would be one direction the second direction that you would have to go is to locate all the all of the sensors that share the five volt reference circuit and start unplugging them but playing our odds here we're going to go computer powers and grounds first because most of the time that's where your problem lies so go into the computer next this is where it helps to have a good wiring diagram this is a Mitchell on demand wiring diagram so thank you to Mitchell for these create diagrams that help us after market guys tremendously look the reason I like them so much more than the other ones is Mitchell redraws them and makes them all look the same format so I don't have to learn how to read legends and codes to read a wiring diagram on say a Honda compared to a GM they look exactly the same to me definitely helps us aftermarket guys to have this style of of wiring diagram and what I've done already is I've mapped out my ignition positive feeds right here the two Pink's I have in a pink highlighter and then my four main grounds so we're going to check those grounds we're going to check these two feeds and then there's one more this is kind of a split diagram there's one more right here an ignition positive feed so I have three main power feeds and I have four main grounds I'm going to go inside to where the computer is now and check those locations and give you guys some numbers on that here's a shot of the back of the computer we're in the glove box area and one of the difficult parts about finding computer powers and grounds and matching them up to your diagram is pin location and there are definitely some helpful charts that give you pin numbers that we can compare the backs of the connectors and get numbers and then compare that to colors but what I found to be very helpful is to look at sequencing so what I want to do is look at my wiring diagram starting with with this top area here and we're looking for sequencing you see a one is white a two and three yellow black so there you know in numerical order so we're looking for white to yellow blacks and to Black's looking for that in sequence on the connector and we can actually see that we go back in here and look down at this bottom connector and you see that we indeed have a white to yellow blacks and to blacks and I'll read off the diagram here for the next couple see if we're on the right part of the connector the next wire color would be green and then we have a yellow and then after that we have brown and yellow so right up this side of this connector is where I'm going to do my first checks I'm going to check this first two yellow blacks on pins two and three those are power feeds and then I'm going to check the two blacks those are grounds and then I'll go a little further up and check the brown and yellows at the top those are also ground so I'll be able to knock off all four grounds and two of the power feeds on this one connector take a second here to talk about another variable we are inside the car now and we're going to do some power and ground checks so it's really important that our ground location where we've chosen our ground and by the way this das was ripped apart when we got it looks like someone was doing some testing but in any case this metal bracket that I've chosen for a ground it's metal so you think it's a good ground right well we want to make sure we don't want to guess because the result of these numbers are going to change our direction and where we're going to go so before we would ever check our computer grounds what we want to do first check one of the power feets and that will kill two birds with one stone one will be that will let us know that we have a good power feed and two it'll also let us know that our ground selection is good we don't want to do ground to ground voltage drop tests when we have a questionable ground on our multimeter so check your power feed first make sure your meter reads 12 volts which tells you your ground location is good which is critical for further testing all right there's a shot of our first power feed it's twelve point two six volts so that is good moving to the next one okay you see I'm on the next yellow black wire up pin three quick comment on these computer pin connectors don't be real aggressive with this deep in some of these connectors are very easily damaged by back probing with a T pin and then also if you're not careful when you don't go straight in you can cross feed one path into another so you have to be very careful so checking my next power feed wire okay there's our second power feed is twelve point two six volts I'm going to do the four grounds on the same connector next alright I got the first black wire t pinned and a hook to that one get you up to the scope and I think what I'll do the rest of the way rather than going back and forth I'm just going to keep you on the scope so I'll go with with the first black wire and then I'll go next to it is another black wire and then I'll come up to the top of the connector up here where these brown and yellows are and show you the scope reading on all four of these grounds alright here's the first of the four grounds see I'm reading negative point zero two I'm not worried about a negative voltage that just means my computer ground is actually better than the ground point I've chosen on my multimeter nothing wrong with that ground now one of the things that you worry about is are you even connected can we trust our voltmeter doing ground to ground voltage test well remember the key is on so it is a loaded circuit that's critical and then the other key with this would be to disconnect your lead from where you're connected so I'm taking my yellow lead off and you see all the noise that's in that pattern now that you didn't see a second ago the other thing you can do is you can shake your lead which kind of increases that noise and then when you connect to the circuit all that's going to go away watch I'll connect back up to it again so you see the difference between a good ground and a no connection is clearly visible so that is a good ground and to save some time here guys every single one of my grounds read this so really we have one more power feed to check and then what we're going to say is all of our powers and grounds are good so we did most of our power and ground checks down here this bottom connector my final power feed is all the way up here at the top to another black yellow wire get your reading on this one okay as you can see we have 12 volts on that one as well so we have all good powers and grounds on this vehicle alright next step in this process is we want to map out this five volt reference circuit being that our computer powers and grounds are good our concern is that we have a short in this five volt reference being we have low voltage on our TPS at this location so what I've done I've already mapped this out but I want to just share with you my thought process we're looking at a three wire potentiometer right here and a 3 wire potentiometer has a 5 volt reference signal on the ground and certain things can be shared in certain things cannot be shared with potentiometers and thermistors and the first thing would be we don't share grounds you can see that this wire right here goes to a splice and is shared between these two thermistors so I know for a fact that that's going to be my ground circuit the signal is on the wiper and so we know that this wire is the signal wire and that means that this final wire is the reference and you see a splice here that we share this reference with another sensor so mapping this out you see it comes over here and comes over to my main shaft speed sensor which would be part of the automatic transmission so the main shaft speed sensor and the TPS both share the same reference wire that comes back to the computer where I have this pink at this location right here the computer coding I can't even read it anymore VC I'm sorry I drew right over top of that it's not important for the coding I think it's VC C - VC is a common abbreviation I know on Toyotas for a 5 volt reference circuit the VC circuit alright there's other sensors that use a reference though and that would be our map sensor so our Maps going to have a 5 volt ref and I followed that one using the same principles what can be shared what cannot be shared and you see that that map comes up to a splice up here comes over to another piece on the transmission this is my counter shaft speed sensor so both transmission speed sensors share a reference one with the map one with the TPS and what looks like two separate reference circuits really is not this comes back to the computer and they come in two locations and I've seen this on other cars what you think is to separate 5 volt reference circuits is actually not it is shared internally at the computer so my next two checks are going to be to check both of these reference wires right at the computer back to our diagram again we're on actually the same connector we're looking for a yellow blue and a yellow red and I actually found them using sequencing again we're on the same connector that we were on when we did our power and ground checks so they get you a shot on it and the yellow red and yellow blue is right next to the two brown and yellows which were my two grounds those are my 5 volt reference circuits and if I am correct in what I'm saying that these are shared and there's only actually one 5 volt reference what we're going to find is the same voltage level on both wires so I want to get you a shot of that next are no changes to voltage scale so you can see it a little bit better this is my first 5 volt reference wire I'm reading one point seven volts that's the same wire we were at on the TPS now we know which one on the TPS was our reference it was actually the yellow red I'm going to drop down now to the yellow blue and get you a voltage reading on that one so one point 701 all right now here's the shot of the yellow with a blue which is our other reference circuit and it's the same exact number so what we know for sure is that the computer is sourcing out two separate 5 volt reference circuits but they are tied together internally and what our suspicions are is one of these sensors that share this reference is shorted to ground or we have a short to ground in the harness somewhere this thing having an engine put in it could very well have a harness that's pinched so our next process here is going to be to unplug these sensors one at a time and watch our 5 volt reference circuit as we do it and hopefully when we find a shorted sensor this 5 volt reference will return and we're going to go into the hood now and start with the easy ones to get to all right I move my multimeter lead back to the TPS under the hood just because I'm under here working it's easier to watch this 5 volt reference circuit from outside remember that our red and yellow and our sorry our yellow and red and our yellow and blue are two separate 5 volt references but they're shared internally so it doesn't matter which one you go to pick one I'm going to stay on the TPS because it's the easiest to do and what I'm going to do is reach down and unplug the TPS first as I keep you focused on the meet heart so you see our same 1 point 7 volts I'm going to reach down and unplug the TPS while maintaining my connection here I'm not going to take my back probe tool out we're just going to stay monitoring the TPS their TPS is now unplugged and I'm still at 1 point 7 volts so what that means is it's not a shorted TPS and what I want to do from this point because I may have to do some short to ground test with an ohm meter when I'm done is as I unplug these sensors I want to leave them unplugged so I can do further texts later in case I don't find a shorted sensor so I'm going to leave that TPS unplugged I'm going to go to the next easiest sensor which in this case is the map sensor the to transmission speed sensors are a little bit difficult to get to we'll go to the map next I'll get you a shot where that's at and come back to the meet can you see our TPS to the right you see I got that connectors unplug just kind of sitting there and map sensor is down here I'm not going to move my multimeter lead I'm going to stay where I'm at on that yellow and red even though the map has a yellow blue as the feed again I said it's the same circuit so I'm going to stay there focus you on the scope while I unplug the map sensor okay back on the beam er you see I'm at one point seven volts I'm going to reach down and plug the map sensor as soon as I unplug the map sensor I actually heard the fuel pump run I buried my scale here I'm at four point nine nine six I'm going to take take this and dump that up to a ten volt so you can see it and again I'm measuring the five volt reference off the TPS while I have the map unplugged and what this confirms is that we have a shorted map sensor our map sensor was pulling this five volt reference to ground not all the way but enough to interrupt not only the signal circuits for the sensors but also that communication link it uses that same five volt reference circuit for communication this is the same stuff I have listed in I believe it's section 10 the 5 volt reference circuit in my book where we go through this procedure and we identify whether or not we have a sorted reference circuit causing our no start condition and that's exactly what we had had we gone through spark and injection pulse and all that we probably would have found that we didn't have any of those I didn't check them because of our direction that we found right away we didn't have this 5 volt reference so we didn't go through all those steps we got lucky in that the second sensor we unplugged was the shorted sensor we didn't have to go to the transmission but if you think about this logically this does match an engine swap when this engine was replaced the TPS in the map I'm sure came with the junkyard engine this car did run before and didn't run after it was installed and it just so happened that we have a shorted map sensor that's pulling this whole circuit to ground now last thing I want to do is to see if the car actually runs and I know it won't run great with the map sensor unplug that's a critical input but I just want to see if the car starts so I'm going to plug the TPS back in and you see our 5 volts is being maintained there that's good I'll show you one more time plugging the map in what it does to that 5 volt ref as soon as you plug the map in there you go sorts of ref out so that gives you a little bit insight to how highly protected I think these reference circuits are that it isn't just like a regular 5 volt regulator you buy from RadioShack that you shorted the ground and you kill it they put protection circuits in here for this these cars are designed to basically have issues and protect the computer I think you're seeing that protection take place so what I want to do is I'm going to shut the key off to kind of reset the computer for a couple of seconds and I'll try to start it can I get one of you guys to do that for me Jeff shut the key off well yeah and give it like five seconds and then try to start it just wanted to power that computer down and give it a wake up when everything is alive and talking guide and try to start it very nice now this thing again won't run great with this map that you're unplugged without is hit confirm fix good and shut that back off shorted 5 volt reference circuit how important is it to know the process we went through when you see something like this I think it was critical and it's going to be it like I said a great review for I believe it's section 10 it might be section 9 that I have all this stuff listed down in order on how to do this you don't see these often the last couple that I did was a bad ground bad power but when you have a shorted sensor like this man it can really throw you for a loop so Rogovin hope you liked it you

Channel: ScannerDanner

Views: 261,431

Keywords: Honda, Auto Tech, auto repair, voltage drop testing, engine performance diagnostics, DIY auto repair, no fuel pressure, no spark, Rosedale Tech, auto tech training, mechanic school, Engine Performance Diagnostics, how to test a MAP sensor, how to test the 5v reference circuit, 5v reference circuit short, shorted 5v reference circuit, no start, no injector pulse, flashing check engine light, 2005 Honda Element No Start, No Communication (case study)

Id: za13UnpbH7E

Length: 28min 26sec (1706 seconds)

Published: Thu Apr 04 2013