Audi P0638, PWM/Duty cycle explained

[Music] [Applause] hi everybody and welcome to new episode of diagnose damned today we're working on this Oh 9 out q5 with a 3 liter v6 TDI diesel engines and the customer complaint is the check engine light is on so let's diagnose this together now first of all let's look up the scan tool and see what Coach we have now I've got a throttle actuator bangwon reads performance all and I've got to eat your circuit Falls in this video I'd like to concentrate the throttle actuator control bank 1 range performance all now when you read a diesel engine you don't wrap it by opening the throttle plate you rev it by injecting more fuel so you might wonder why does a diesel engine be the throttle body in the first place and that's actually a very good question there are three main reasons why a throttle body is used on a diesel engine when you shut down a diesel engine you do it by cutting the fuel now a diesel engine has got a higher compression ratio than a petrol engine and because of the high compression when you shut it down it tends to shake when you stop the engine now by installing a throttle body it allows you not only to cut the fuel but also cut the air supply resulting in a lower compression and a smoother shutdown now in this particular model the EGR gasses get sucked into the engine over here now typically inside the intake manifold of a diesel engine there's no vacuum making it very hard for the EGR gasses to get sucked into the intake manifold now by installing a throttle body we can temporarily restrict the air flow into the engine creating a pressure drop for better each your performance the third reason we need a throttle body on a diesel engine is to regenerate the enou extent to regenerate a nmuk scat we need a slightly rich mixture we achieve it by using a throttle body to temporarily restrict the air flow into the engine creating a rich mixture now that we finally know where the throttle body on this diesel engine is for can we finally diagnose the thing now the throttle body lifts in between the intake manifold and it's turbo hose over here it is held down by three screws and a host clamp so I got it out of there but I left the connector attached to the throttle body so electronically it should still work I'm going to use the scan tool to bidirectionally control the throttle body and command it to close and now that it's out of there it should be easy to see if there's any response I'm gonna command the throttle body to close so let's see what happens when I hit the start button it should so let's see what happens and as you guys can see there's absolutely no response from the throttle body now that we know our frontal body is non-responsive the next thing we should do is take a look at the wiring so let's take a look at a wiring diagram and do some measurements so I've looked up the wiring diagram put a specific engine let's find throttle body and it is actually over here it is m24 and we can see it in on pin 1 there's a ground on pin 2 there's a power coming from this 15 amp fuse over here and there are two communication wires running in between the throttle body and the BCM let's start out by checking the power in the ground wire coming to the throttle body so let's back probe the ground wire on pin 1 and the power feed and pin 2 and if the power and the ground are okay my test light should light up [Music] now when I took a look at the wiring diagram of this throttle body the little transistor symbol drawn into the throttle body indicated to me this throttle body isn't just a motor and a potential meter it's actually bit smarter than that the other two wires besides the power in the ground are actually communication wires one wire is coming from the PCM to the throttle body and it's commanding it to open and close the other wire is a feedback signal to report back to the PCM if it actually did I've got pinched three and four back probe at the throttle body so let's start the measurement and let's zoom in a little bit now let's use the scan tool to command the throttle body to close again and we can actually see the command changing from opening to closing now if we zoom out from a recorded waveform we can actually see what the other channel has been doing and the other channel created this waveform telling the PCM it didn't open or close now that signal we stopped coming from the PCM commanding the throttle body to close was actually a PWM signal now to get a better understanding of this signal let's learn a little bit more about PWM or pulse width modulation to get a better understanding of PWM I'm using this blower motor and it's jump starter as a power source I've got the negative side of the motor connected to the negative terminal of my power source now we all know that when I connect the positive side of the motor to the positive terminal of the power source the blower motor is going to run at full rpm if I want to slow the blower motor down I can achieve this by briefly touching or pulsing the power source now as I was turning the blower motor on and off you could see the RPM of the motor wasn't very steady now that's because I'm not precise or fast enough so in the next test we're gonna use this tool which I got from Ryan automotive and I will leave a link in the description of this video it is a great tool for diagnosing systems that use pulse width modulation in this test I've got the blower motor hooked up to the tool and a to hook up to the power source now let's do the same thing as we did before but let the tool do the posing for me [Music] [Music] now this tool used the pmw signal to increase and decrease the speed of the blower motor but to exactly understand halves doing this we've got to learn more about the basics of pulse width modulation a pwm signal uses a fixed frequency frequency is expressed in hurts and hurts is the number of times something occurs within one second now it isn't the frequency or the number of times we turn the motor on and off that's causing the increase or decrease of the speed but it's the actual on time now to get a better understanding we need to look at a waveform of our pwm signal now since PWM signals aren't only made to drive blower motors in the next test we're gonna use an EGR valve with the tool we can test this EGR valve by opening and closing it [Music] I'm driving to eat your right now and let's count the number of pulses on the screen 1 2 3 4 5 6 7 8 9 10 11 12 13 now the screen time is 100 milliseconds this means there are 10 of these frames within one second so 13 multiplied by 10 means a frequency of 130 Hertz now you can easily check the frequency using a multimeter just put it on a Hertz reading and the reading right now is 130 Hertz this means this valve is being turned on the knob 130 times each second now let's open this EGR valve and in the meantime take a look at our waveform now the frequency should remain the same at all times so the same number of pulses across the screen at all times now although this valve is being turned on and off 130 times each second you can see there is still time in between those pulses now the time this valve is being switched to a power source it's called the on time and right now this is close to 0% now the time this valve is not being switched to a power source or the valve is off it's called the off time and right now this is close to 100% now let's open the EGR valve and look at our waveform [Music] as you saw in the example the frequency of our signal remained the same the only thing that changed was the on and off time of our component now this is what we call a duty cycle and a duty cycle is expressed in a percentage a percentage of on time now in the next clip I want to show you three examples of duty cycles the first being close to 0% the second being close to 50% and the third duty cycle being almost 100% at a zero percent duty cycle the component is never being switched to a power source so it won't work now at a duty cycle of 50 percent the component is being switched to a power source half of the time so it will work at half its potential now at a duty cycle of 100 percent the component is constantly being switched to a power source and it will work at its full potential now if you haven't got a scope but if you want to check the duty cycle of this EGR valve to see if it's being commanded on or open you can still use a multimeter which can read duty cycle now in this tool there's a dial that goes from 0 to 100% now let's dial up the duty cycle and what's the reading on our multimeter now we already saw the duty cycle is a great way to control EGR valve or a blower motor but there are countless other applications in your amount of industry I want to show you two more let's control throttle body using duty cycle and remember the old days we had separate Lightning bulbs four separate functions for instance lightning and a brake light now using duty cycle we can combine these functions in one single light bulb by altering its brightness so one moment it's your lightning and the next moment it's a brake light we have got to talk about one more application of pwm signals and it might be the most important application for diagnosing or Audi pwm signals can be used as a form of communication now let's use our Audi as an example the PCM is not directly controlling the throttle body motor that's up to the electronics inside the throttle body itself but the PCM is selling the throttle body by duty cycle what percentage of throttle valve opening is desired so in this example the PWM signal or duty cycle is not controlling the throttle body but it's used as a form of communication now we verified the power and we verified the ground and we actually saw the PCM commanding the throttle body to open and close so I decided to take a closer look to this throttle body and this is what I found actually a hole burned into the electronics inside the throttle body now since her old father body was fried I ordered a new one so let's install it and let's command it to close again and see if it works I'm curious I'm really curious another one diagnosed and fixed and we got to learn a little bit more about pwm signals interesting right now if you liked this video and if you want to learn more please subscribe to my channel and when you hit the bell you will get a notification each time I post a new video diagnosed then fixed it again see you next time guys [Music] [Music]

Channel: DiagnoseDan

Views: 122,937

Rating: 4.9679575 out of 5

Keywords: Gmto, Bmw, Audi, Diagnose, diagnosedan, scope, pwm, pulse width modulation, duty cycle, mechanic, educational, technician, fix, diagnostic, scotty kilmer, eric the car guy, scannerdanner, chrisfix, south main auto, robinson auto, astral auto repairs, weberauto, repair, faultcode, scantool, snapon, new level auto, humble mechanic, engineering explained, racheds and wrenches, ryans automotive

Id: yxjcBO4V8Uk

Length: 22min 56sec (1376 seconds)

Published: Sun Jul 15 2018