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EGR sensor and PCM interaction

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01 Dec 2019 14:32 #35484 by EventAlchemy
EGR sensor and PCM interaction was created by EventAlchemy
I have been wondering about this subconsciously but never brought it up.
I understand that the PCM gets its signal from say a particular sensor and then the PCM decides what to do after it gets the signal.
For this, I will just take EGR solenoid position sensor to illustrate what I mean.
I assume that the computer expect that the EGR position sensor instantly sends some sort of signal to the computer when the engine is starts. So I assume that so long as it is receiving that signal, the computer will not do anything in regard to that signal or engage in anything more in regard to the valve.
I then assume when the position sensor tells the PCM that it is sensing temperature exhaust or whatever, that is when the computer decides what to do with the valve. When the computer executes its message and it is not getting the same reaction back, it will inevitable throw whatever code that is needed.
So the question is, what if the position does not send any message at all in the first place after its initial good morning, I am here at work and alive. How would the computer do anything or would even know if there is anything wrong in that system?
It is like you tell someone, " let me know if you need anything". And "if I don't hear from you, it means everything is okay" but " just be in touch every morning so I know you are alive and at work, otherwise I would think you are dead and that is another story which then I have to hire someone else".

I assume that there has to be other things that the computer uses, other signals from other sensors as reference, a sort of a sign that say the EGR valve should also be doing something and it is snoring on the job, not paying attention so to speak. It is not sending me signal or whatever.
So I would think this is a collective action from multiple sensors that the computer uses to see if any particular sensor is not playing with full deck. However I would think that some malfunctions of a particular sensor the computer would know directly from direct interaction with that sensor.
Do these assumption of mine have any sense? I am no t a mechanic. It is the curiosity in my head that throws these things at me.

And on another note since I used the EGR valve for the example.
Everywhere all I hear and no one seem to go beyond it. It is the Position sensor that is ends the conversation as the ultimate entity that detects the EGR operation one hand and on the other communicates with the computer. The messenger, the go in between.
But why does not one say anything about where does the sensor gets its sense.
I have extreme difficulty that it is this so call position sensor that is first in the line of exhaust temperature ( or whatever sensor or detector).
I think it is something much more basic, something physical, actual. And I don't think it is even whatever the sensor touches either because to my feeling whatever it touches is something solid. That is not either. It has to be something to expands and contracts, something like a spring, like the spring in a thermostat for the engine's coolant system or some such thing. If this is true, why no one says it anywhere at all?
Or is it that it really goes without saying because everybody simply knows that as a simple common sense fact like everybody knows that we breath all the time so why would anyone have to say it except once in a blue moon when you have to check if someone is breathing or not in case they look dead or something?
If that is the case and everyone mechanic or not simply know that, this means I am way, way slow upstairs and have a lot of catching up to do.
I wonder if they say it even in a classroom and even there they stop at the EGR position sensor as the main entity in charge. Or is it that a spring is not very glamorous of a term compare to an academic term; i.e. sensors, signals, duty cycle, modules, references, and the like.....
I don't know.. I don't know.
Thank you in advance for your comments and take on my plight.

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01 Dec 2019 16:36 - 01 Dec 2019 16:38 #35492 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic EGR sensor and PCM interaction
The engine computer monitors the health and operation of sensors and actuators in several ways.

One way is they compare the output of sensors and compare them with other sensor, for example for example some computers cross check the inlet air temperature sensor, coolant temperature sensor, oil temperature sensor and ambient temperature sensor to look for something that dosen't fit.

Anotherway is to apply a bias voltage to check circuit integrity this is comonly used on speed sensors.
How EGR valves are monitored varies one method looks at temperature another is to run the test under certain specified conditions (for example when the vehicle is cruising) and look for changes in temperture another is to look for changes (ie reduction) in MAF output and MAP output as the valve is opened.

" Welcome to the 21st"


Last edit: 01 Dec 2019 16:38 by Andy.MacFadyen.

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01 Dec 2019 19:18 #35501 by EventAlchemy
Replied by EventAlchemy on topic EGR sensor and PCM interaction
I just read the above reply and then I went ahead and read my topic.
It looks to me that my subject needs way more editing than I care to mention. It almost look like, was that me that typed it.
I won't blame if someone wonders just what on earth was saying anyway. :-)

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