GMC Yukon HVAC Blower Motor Won’t Turn On

yeah hey guys thanks for joining me today I got my son Caleb behind the camera thanks Caleb for being with us GMC Yukon Denali we're working on apparently the blower motors not working at all so I guess the first thing that I wanted to do was to scan the system see what kind of fault codes we have I don't know if this is a computer-controlled climate control system or not yet so these are just some preliminary things so I'll get you on the scan tool here with me so what I'm gonna do guys is a code scan this is gonna this is going to scan all the mazels for faults okay that was super fast too so a bunch of engine codes got this got codes out the wazoo we're just worried about in the blower circuit I guess we have fuel system rich codes it's still going through I in a wait till it's done while this is still doing its code scan guys what we have is a we do have individual driver passenger controls this is going to be computer control it has an auto button auto climate control it's computer controlled for sure and we have no blower control so the my fan it's a little fan symbol and then the bar we have nothing nothing at all and then we have some weird noises coming from the OnStar speaker system it's just weird anyway all right codes rich codes probably an alcohol in fuel miss compensation or miscalculation is my guess on that evap emission large leak purge flow code breaks which don't care about that transmission fluid pressure airbag system has a fault code front-end sensor we know about those I have a video on some front-end sensors on these GM's they crack look for a link little icon right here next to me that's if this is on YouTube not sure where this video is going yet but I do have some video on the front end sensors and on the alcohol in fuel tests driver's door switch we have some you codes passenger door switch I don't care about any of that electronic suspension through there's codes on every system in this vehicle nice I have an HVAC code says airflow control 10 feedback circuit short to battery or open not totally sure what that means it has a feedback circuit involved with the blower motor that's setting a fault code I don't know if we can get help on that or not be 37 82 that's what we want let's go there first HVAC there it is HVAC so this next question says with automatic HVAC or with manual in the way that you would tell simply is you look at the – and if you see an auto button then that tells you where we are so we're picking with automatic a/c this will give us the same code that we had in that main code list it should why does it say no codes present there this history code being 37 82 so just see if we have do we have a troubleshooter on this huh there it is sweet just need a little info on this without going to Mitchell it says that airflow control feedback circuits short to ground air flow control feedback circuits short to battery or open or actuator stuck says the HVAC control module controls the HVAC door actuators to regulate the air flow through the HVAC system each actuator consists of an electric motor a potentiometer module supplies a low reference 5 volts oh wait this is talking about the mode or not the blower airflow control airflow control see I'm thinking blower airflow feedback that's not what this is airflow control is a mode door in which direction we're moving the doors guys this has nothing to do with the blower motor not working at all this is talking about a mode door and a position sensor signal and again this is not what we're doing either so we're going to attack this like a normal blower circuit it's going to use some type of module that controls the speed or it has a resistor and then the blower motor itself so this should be pretty straightforward I'm actually gonna try to stay low-tech here first just gonna go grab my test light unless I can do something else with the data let's see what kind of data parameters we have inputs so when a blower motor doesn't work with talking about a switch the inputs we're talking about the motor itself and then the resistor bank or a Mazal some of these will be pulse width modulated fan down button nice ok cool so I'm looking at fan down button this one right here and I'm looking at fan up button and if when I hit this it says inactive right now if I hit the down you see it goes active if I hit the up it should go active and so there's a real nice fast test for the switch itself this computer is seeing this there's no issue on the input side now we're on the output side on/off AC auto mode defrost good there let's go back to a functional test see what I can do here with a functional auxilary blower motor auxilary blower motor should be the rear if it has one does this have rear air I do not see a rear air setting there yes it does okay there's blower motor so I said I was staying low tech and grabbing my test light but if I have the scan tool connected and I can do this kind of stuff this is pretty cool so this is one where I can command the blower motor to turn on so I'm gonna do that right now nothing so we're on the output side when you have a bi-directional test like this what this tells you is that we do not have an input problem so when you let me restate that when I take a scan tool like this and I bidirectionally I'm turning the blower motor on and off what I'm doing is I'm bypassing any switch on the dash so anything here on the dash really eliminates that on the output that I'm doing eliminates these inputs it's still not being controlled we have an output issue okay inputs are fine we already know that just teaching some other aspects here all right so that's not really helping me I'm back to doing our text at the motor I need to get some test equipment blower motors right here so I just got to take this bottom panel off okay so some basics this device right here is controlling this would be my my controller it's either a resistor or it is a module I don't have a diagram right now and that is controlling the blower speed blower motors right here so the purple wire and black wire would be the two wires that go to the motor that would be a power in the ground just a real fast power and ground check right here is where we're gonna start and I said I was going to use my test light but I am choosing not to because I have my verus already synced up here it'll be a lot easier for you guys to see what I'm doing by using the voltmeter part of the verus so you guys that are following this video you don't need to have this expensive scan tool to do the test that I'm about to show you just a simple voltmeter is all that's needed okay I gotta find a known good ground went to a metal bracket on the dash we do not know if it's known good yet find out here in a second I'm just gonna go to my digital multimeter again if you have a voltmeter you can do this test going to the the purple wire first just back probing the connector right there has battery voltage on it 11 3 and is that low because the battery is weak most likely there's 11 6 so what what I want to do before I check the ground I want to see if I can make that voltage go away now the way these blowers are controlled again I'm not using a diagram just not common knowledge will either control the ground side of the blower or will control the power side of the blower and what I was gonna do next is turn the blower off and see if my voltage goes away if the voltage stays there then I'll know it's being controlled on the ground side if the voltage goes away I know it's being controlled on the power side so there are variables to this I'm getting ahead of myself let me do my checks and I'll explain to you guys what I'm doing so I have battery voltage there go on the ground wire real quick this is the opposite wire the black wire and look like I had voltage on that too and you'll notice I'm doing this plugged in I'm back probing it that's my let's see there's power 11 6 yeah it's there's voltage on the ground side so what that tells me is this blower motor is not being controlled right now and that voltage is fluctuating too very strangely so in other words the the test I've done so far say this is not a bad blower motor this is a controller issue right here not there's some variables here but that's first view I don't like the way this voltage is fluctuating either what I'm gonna do now is I'm going to turn the blower switch off and we're gonna watch our voltage here so we'll just go that is off they see went to 11 v with it off this is definitely being controlled on the on the ground side of this circuit you see the that's with the circuit on up here on the – blower on high turn the blower speed down alright so what I need to do now guys is um I could be wrong about what I'm saying here this could be a pulse width modulated circuit and our voltmeter is not fast enough to show it to us so I have to go to my graphing meter now or we can go to our lab scope because it might be a really signal that the graphing meter doesn't have a time base to show us but you guys that are using a regular multimeter can still focus on this 11.2 number but now I have the ability to look at actual signals peak detect is turned on I'm on a five-second screen so I shouldn't miss anything with peak detect on and I'm really not having any changes here whatsoever as I'm moving the blower speeds up and down there's low speed right there and there's high speed so really no activity at all sorry you want to see that digital number to get that back on the screen no real changes here guys all right so I could ground that circuit right now make this blower a run is what I'm what I'm saying maybe I'll do that but it looks like our resistor is faulty let me do some text on the other wires we just need need to have this module replaced there's only three other wires so the other three wires for this this is not a blower resistor this absolutely is a module we'd have a power and a ground and then this wire the small gauge wire is my only control so that's the one we want to focus on too but let's get a quick reading of the main feed coming in there's 11 5 and then the main ground this should be near zero volts there's zero the hash that's in the signal is because I have peak detector nan and I certainly don't need to be on a 50 volt scale here won't change anything where we are but so good power good ground and this is my control pin yeah it's a pulsed signal and let's change our time base here so you guys can see this and we'll put a trigger in here to make that steady what we should see I'm going back up here what we should see with this is as I am changing my blower speed we should see different pulse widths and I know that you're not really seeing that now Kayla because you're focused on me but notice the pulse width change means my commands are here the signals are here computer is working fine the HVAC computers working fine what it's doing caleb is this the HVAC computer is actually part of this cluster so it's literally right behind here and what this is telling us is the HVAC computer is telling this blower module what to do and the blower module controls the blower motor so what this tells us by this signal changing as I'm changing the fan speed is there is nothing wrong with my HVAC computer there's nothing wrong with the signals coming down to my module there's nothing wrong with my module powers and grounds that's the blower module for you guys that aren't familiar with what I'm talking about the blower module for this car would be the equivalent of a blower resistor this is not a circuit that drops voltage by using a resistor it is actually pulse width modulated the blower motor to control its speed and that's what this is right here the signal from the HVAC computer is signaling the blower module what to do the blower module has a good power and a good ground we're done it needs a blower module it's really that that simple we're finished already with this one will will back it up with one final thing which is me energizing the blower motor myself but as you can see this is fan speed on low we have a certain pulse-width signal and then this is as I scroll up there I'll go into increments there's a low there's the next step up next one up that's third speed there's the fourth speed v and then there's high okay so it's telling the computer what to do computer being the module the module is controlling this blower motor by the ground side of the circuit I'm pretty confident in that let's turn this trigger off I'll put it on auto and then change our time base this is the I just I need to get my polarity here for a second that is the ground of the motor and the ground is this is the one that should be being pulsed right now and it's not and then the feed right 11/5 let me unplug this and get two readings on the pins of the module itself yeah that's the ground pin and that's my power feed so it's definitely ground side controlled with it uh ha just made it turn on you need to put a residual in this Pete okay or is it yeah it's really not a resistor in this case it's a it's a module but yeah when you order the part you can ask for a blower resistor it's not a resistor it's just by me unplugging it and plugging it back in on the connector it came back to life yeah just two bolts I'll bet two that's one you probably could pull apart and resolder a crack solder joint is my guess but let's look at these signals now this is on the ground side of the circuit we're reading point two four that's blower on hi this is blower on the next one what we'll see is our voltages are gonna rise here and you can see that that's exactly what's happening this is what it should be doing and that's with the blower on low and then when I turn the blower off that should go to full battery voltage let me change my time base a little bit longer so you guys can see that let's go ten seconds this is a ground side switch circuit guys hope for you guys that need more info on what I'm talking about and how I determined that the ground side is being controlled on this this is chapter three material scanner dander premium chapter three material or Chapter three in my book I cover power and ground side switching what I did is I had two readings I had twelve and twelve okay unplug the connector I read 12 and zero told me this is ground side switched and what our issue was this module was not supplying the ground that it needed to for the motor itself we proved the module has good powers and grounds itself and the motor power and ground was where our issue is no ground on I don't think I'm making sense here there are two sets of powers and grounds and then there's a so there's four wires to this come down here to get my hand alright just want to make sure that I'm clear on what I'm saying here to you guys um this is a module this module any module to work needs a power in the ground the main power and ground of these two guys right here those were good we had 12 volts on this red one and we had zero volts on this ground with the blower being commanded on the computer was telling this module what to do on this small gauge wire we checked that one we know that that's those signals are good computer was telling this module turn the blower on and it was not we did some measurements on these two wires the other two power and ground wires this is the blower motor power in ground and we determined that it's ground side switched and the module was not turning the ground all into the motor so when you see something like that you have to make sure that your module has good power and ground especially the ground in this circumstance this one was low all the time at the same time this ground was high telling us the module was not grounding the blower motor okay the only option then would be to make sure that your computer is telling the module what to do and it was all right keep in mind the power on the purple wire comes actually from the red wire the red wire goes inside into the module wraps around comes out on the purple constant power on the purple and a pulsed ground on the black motor control circuit that's the one that I was just on right now that's the one I'm gonna show you one more time this is normal circuit operation and all I did guys was unplug it plug it back in right there that sir at that connection so what that tells me is inside this module you got a bad pin all right focus on the screen now this is circuit off voltage right now eleven point five is my circuit off voltage right ground side switched no ground normal ground voltage with no ground 12 volts turn the circuit on and this is the blower on the lowest setting you see a slight drop in voltage we're giving this motor a partial ground right now it's you can actually see the fuzz right here Caleb you can see that our blower motor is working the lowest speed right now okay and we have less than battery voltage less than battery voltage this is blower position to notice the voltage dropped even lower we're giving a better ground my little piece of fuzz here is blowing more you don't need to zoom in on it but okay it's working next step okay dropping voltage again each time voltage drops we're giving a better and better and better ground that's what's happening here the next step next step and then here's your high position now what's cool is I can show you all of that on the screen together each one of these steps so this is circuit off this is low two three four five high that's how it should work nothing wrong with this blower motor guys I don't need to now manually energize it it's just an issue with the module itself we're done it's really that simple can we take this module apart and see if there's a crack solder joint hell yeah we can I'm gonna try it be real quick because I'm calling this motor is bad and we're gonna change it of course but this would be a good lesson on on crack solder joints if this has one I'm pretty sure that based on the fact that it worked as soon as I unplugged it and then plugged it back in kind of tells me that we're dealing with a circuit board issue I know some of you are thinking what about the connector itself but you saw me just look at it there's nothing wrong with this connector no corrosion the pins aren't spread a heart and we got nothing like that going on these things are really susceptible to heat think about what this module does it carries all the current flow for this blower motor and it's constantly pulsing on and off well technically input that's pulsing the yeah we can't we can't do anything with this the these are all cooling fins Caleb and there really is no taking this apart I don't think what's cool is I was able to show you guys a working circuit I don't care if I break it cuz I did break it yeah I can't see this with my naked eye I'm freaking blind got my readers you know someone who is more patient than me today cuz Caleb's got to go I don't see any cracks or joints but does not change our call nice easy diagnosis on a blower inop blower circuit on a GM pretty standard practice some people are afraid of computer controls you know they'd rather have old-school resistors guys that was easier to test than a resistor bank two main feeds one computer control and then two wires that go to the blower motor blower you call this a resistor it's really not a resistor it's a module this module controls the pulse width of the blower motor for more information pulse width modulation duty cycle controls power ground side switching module to module communication voltage drop measurements how to know if a circuits power or ground side switched scanner danner premium it's available on my website there's a 14-day free trial you guys can check it out I teach at a Technical College rosedale Technical College in Pittsburgh Pennsylvania you guys could check us out there too but come over to my website I've recorded all of my classroom lectures I talk about all of this stuff can reinforce this further for you guys pretty standard troubleshooting procedure on this vehicle foundational information that's what I focus on you guys have been following me long enough know this so come check it out that's scan dan or comm scanner Dan or premium click on the scanner Dan a premium tab there's a 14-day free trial hope to see you guys there Thank You Caleb for being my cameraman today everybody can say thank you to Caleb we'll see you guys next time

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