Custom PID - ECU explanation

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PitrsRS
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Custom PID - ECU explanation

Post by PitrsRS »

Hello Harry,

I want to ask about ECU definition in Custom PID section. I understand things like, PID, Mode, Formula etc. But what I still don´t understand is ECU selection. You mentioned there $21, $22, $23 but what does it mean? I´ve looked into documentation, but there is only $22 mentioned for Ford cars and steering angle.
I´ve looked in PID OBD on Wiki, but there is nothing like that. What if I have VW? Which one will be correct? Or I just try it?
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Re: Custom PID - ECU explanation

Post by PitrsRS »

So, I´ve tried to change "ECU" from $21 to $01, without any change - I´m testing it on fuel level. What´s strange is level of fuel. Car says approx 55-60%, HLT "only" 44-42%. So, where is the reality?
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Harry
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Re: Custom PID - ECU explanation

Post by Harry »

$21 etc are not ECU selections, but OBD modes (like 1 and 9 used by default).

ECU selection is often required for custom PIDs. They will not be answered when broadcasting requests (which is the default). It will almost always be fine to use the symbolic names "ECM", "TCM" or "ABS" instead of the protocol specific addresses.

The most relevant part of my answer is: VW doesn't publish there custom PIDs (if any), they will likely use other modes and will be encrypted. I have not seen useable information for the VW brand.

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Re: Custom PID - ECU explanation

Post by PitrsRS »

I see, and is there some list of "symbolic names" for example for engine unit? It´s ECU or ECM?
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Re: Custom PID - ECU explanation

Post by Harry »

ECU is the generalized term for any control unit (Engine Control Unit).

ECM is Engine Control Module
PCM is Powertrain Control Module and used as a synonym for ECM here
TCM is Transmission Control Module
ABS is the Braking Control Module

I think PCM is actually a broader term and usually names the group of ECM and TCM.

From an architectural point of view, all of these are not well defined. Cars come with all combinations of control units. Often with multiple or combined units. And almost always connected with multiple busses. But there are conventions to map the main ECM / TCM / ABS units to physical addresses. This is what is used by LapTimer.

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Re: Custom PID - ECU explanation

Post by PitrsRS »

Thanks, for my purpose ECM will be enough. I don´t think its possible to get data from DSG (TCM) or ABS in VW... :roll:
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