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OBD PID explanations.

  • steve86
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06 Mar 2019 20:26 #27636 by steve86
OBD PID explanations. was created by steve86
Hi all,

Reason for this post is that im currently looking at my throttle position sensor to see if it requires cleaning and an idle relearn. I have noticed that there are a few different throttle PIDS.

I.e Relative Trottle position, Absolute Throttle position, commanded throttle actuator, ect.

Can anyone explain or point me to the right direction as to what these mean and which one I would be using for my throttle plate position. Thank you.

Kind regards
Steve.

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07 Mar 2019 15:55 - 07 Mar 2019 16:15 #27647 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic OBD PID explanations.
All very involved in a drive by wire system, just remember the driver tells the engine computer how much throttle he wants and the engine computer decides how much to open the throttle in response.

The desired throttle position is the the engine computer wants the throttle butterfly to move to.
The actual throttle position is exactly what is says the actual percentage opening of throttle butterfly

Also in a drive by wire system gasoline (or diesel) engine the accelerator pedal as two position sensor as a fail safe sanity check. The two senor outputs work in opposite directions 0-5v and 5-0v.
The throttle butterfly position sensor on drive by wire throttlebody has similar 0-5v and 5-0v sensor outputs.

"Speak Softly but carry a Big Test Light"


Last edit: 07 Mar 2019 16:15 by Andy.MacFadyen.

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  • Tyler
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08 Mar 2019 21:46 #27676 by Tyler
Replied by Tyler on topic OBD PID explanations.

steve86 wrote: I.e Relative Trottle position, Absolute Throttle position, commanded throttle actuator, ect.


It's kinda confusing. :silly: The way I understand it, Absolute Throttle is the unlearned value of the TPS sensor. It's always gonna read something, even with the throttle completely closed.

Relative Throttle is the throttle position compared to the learned closed position. As in, if 9% Absolute is with the throttle fully closed, then Relative will read 0% in the same position.

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09 Mar 2019 16:15 #27696 by steve86
Replied by steve86 on topic OBD PID explanations.
There is also a throttle position b to. They do sound confusing lol, Thanks for explaining guys! Cheers.

Steve

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  • Tutti57
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Today 20:23 - Today 20:26 #27968 by Tutti57
Replied by Tutti57 on topic OBD PID explanations.
How can you use these values while trouble shooting? I never really know what to do with them.

While we are on the topic of PIDs, what the heck is STFT sensor 1? I understand bank 1 but see sensor 1 sometimes too, maybe as a high percentage like 99%.

Sent from my Moto E (4) Plus using Tapatalk

Lots of diagnostic gear.
Last edit: Today 20:26 by Tutti57.

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Today 20:50 #27970 by juergen.scholl
Replied by juergen.scholl on topic OBD PID explanations.
To get a grip on the absolute/relative tps have a look at page 32:

www.scannerdanner.com/media/kunena/attac...5B43B_2019-03-20.pdf


The stft sensor pid shows the grade of authority this specific sensor has on the fueltrim. But be aware that often times a 99ish percentage reading _ especially for the post cat O2 sensor - just means NO fuel trim correction from this sensor!

An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.

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