2009 GMC Sierra Intermittent No Crank U0100 Lost comm with ECM/PCM

all right guys we got it 09 GMC Sierra that is intermittently losing communication with the ECM so right now it has no communication excuse my frame rate service traction control and service stability track it won't start whenever you turn into the crank position it's very intermittent but whenever it does happen we've got our Tech 2 here the uh ACM has no communication we're back fuel pump module had a history code for lost communication but it now has a current code and the transmission module had the same code so and there's a lot of other modules like the BCM maybe the radio the cluster they have all the same codes but for the remainder of the time that it shows the traction control light it will no crank no start so now we just gotta sit here and wait for it to come back alive but while we're waiting I'll show you I've already figured out what the problem is but I'll show y'all how I came to figure out what the problem was so we've got our wiring diagram here once it comes up let me get in the out of the Sun so since it's losing communication with the ECM only I had my breakout box here and I checked it and I had 60 ohms of resistance all the way through so we knew where we weren't having a cut wire that was intermittently losing connection on the can wires uh but we went to ECM and the ECM has let me see here we have an ignition one here on the pink wire a B plus on the red with white wire and then we have an ignition one on the pink with black wire whenever I went to checking which is in the film mode right now I can show you so I got my Power Probe here so I took these connectors off or the the lids off so that we can see it I got a pink wire here which is the ignition one turn my sound on so we got power there the red with white here is the B plus got power there and then we have a pink with black here this is the other ignition one it is grounded so when looking at the wiring diagram that is supposed to be power coming from it goes to 15. 15 goes to 12. 12 goes up to the ECM throttle c-o-n-t fuse five so then I went to fuse five to check if it was popping which I can just use this here [Music] so let's get fuse diagram so fuse number five is right here which is this 15 amp here so whenever we check that got a ground and a ground so the fuse may be popped but right now it's not even getting power so that gets power from the powertrain relay so then I went to the powertrain relay which is right here it's this second gray one here take that powertrain relay out and we've got power there power there ground and ground so if you look at the relay maybe you can see those numbers so with it going in like this we've got power on 87 and 86. nothing on 85 and 30. we may swap those just because of how the wiring diagram says so yeah 85 and 30 are fuse or our powers from the ECM battery fuse and the TCM battery fuse so we've got power there and on pin 30. oops so 86 and 87 are ground which 87 would be ground until the relay clicks on there we go the yellow wire which is a control comes from 14. and 14 goes over to 18. and then 18 goes to 59 powertrain relay control there on pin 59 of the UCM which is the same ECM connector that the pink with black pink and red with white are on so start looking and that yellow wire is right there beside that green one so then take our pinch probe and we'll connect to the green wire and it is grounded so we put our powertrain relay back in [Music] it is power so what's supposed to happen is the ECM is supposed to ground it which causes the coil let me go back to that relay the ECM is supposed to ground it which causes that coil to pull the the switch which then puts power on all of these if you listen I'll turn the sound off just so you can hear it ground it you can hear the powertrain relay clicking foreign so whenever you ground it turn the sound back off ECM is essentially getting power through the powertrain relay so what I did to prove this is I unplug the ECM it's kind of hard to do with one hand there we go and then plugged it back in and whenever I did you could hear everything click there it goes hear everything turned on so then we'll check the yellow wire again so now the yellow wire is grounded which means that we have the powertrain relay back in everything's connected put that there so it doesn't fall vehicle will start as you can see the traction control lights off now starts right up so set this over here so we can hear it for whenever it Cycles off [Music] hopefully this goes by soon [Music] you can see the little green light on the Power Probe the green means ground whenever it switches to red that's power [Music] so whenever the the truck shuts off that'll switch over to Red to show that the ECM is no longer controlling the ground side or the control side of the powertrain relay [Music] it's got an intermittent misfire as well [Music] they originally told me which I'll pull it up here that this was a no communication with the body control module [Music] as you see here body control module is not communicating I get here and everything communicates and it starts right up no history codes whatsoever like they had went in and cleared the codes so I was confused started right up no problems no codes to go off of I went to grab my research laptop come back and the truck was off [Music] with the traction control light on so I went into body control module body control module had no codes you can see that check engine light flicker [Music] still got our ground from the ECM thank you [Music] it acts like it wants to die but then it'll kick back up [Music] I hate that my just sitting here flickering [Music] [Music] there it goes so now you look and it's 12 volts can't really see it but the red light is on that it's 12 volts and it is dead so therefore the ECM is losing the the control is not controlling it anymore so that is why the ECM is bad so now we're just going to tell the owner got to get a new ECM and then they'll call us out to program it cycled the key again darts up engine power is reduced codes is it setting now [Music] nine codes transmission code fuel pump module code throttle position sensor 2 high voltage too low voltage oh that may have been because I unplugged the I unplugged the connectors let me clear the codes real quick and see what's going on engine power is reduced message went away still clearing codes there we go no coats let's turn it back up instantly died no crank all right as always thank you all for watching see you on the next one

Channel: Devon Rice

Views: 75,172

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Id: uBB5hyC5tX0

Length: 14min 35sec (875 seconds)

Published: Sun Oct 09 2022