tonic
Totally Hooked
- Aug 31, 2023
- 197
- 604
To answer your question about tire data: you can't get it without ATCEA2A, and you likely need ATTA2A as well. Without ATCEA2A addressing isn't full to reach the TPMS ECU.
The Long Answer:
When you request data, like engine oil pressure, into RaceChrono, you use these values:
OBD-II Header: 0x700
PID: 0x221074
It's actually a bit misleading. These values really enables communication with UDS (Unified Diagnostic Services) rather than OBD-II. UDS is a much more powerful system used in modern cars.
Here is how those numbers break down:
0x700: CAN ID, the Engine ECU's "address". This varies by manufacturer.
0x22: The UDS service "Read Data by Identifier."
0x1074: The Data Identifier (DID) for engine oil pressure. This varies by manufacturer.
When engine ECU receives this request it responds with value for oil pressure at that moment.
If DID is different, say 0x1638 it will respond with M/T oil temperature instead.
Why ATCEA2A is needed?
AT CEA 2A is an ELM327 command that sets the CAN Extended Address to 0x2A.
0x750 CAN ID you are using for requesting tire information is the address the Main Body ECU and the 0x2A is extended address for TPMS ECU.
Think of the CAN ID 0x750 as an apartment building and 0x2A as the specific apartment where the TPMS ECU lives. Without the apartment number, your request never reaches the right door.
Why ATTA2A?
AT TA 2A helps manage ISO-TP multi frame responses. Basically, it ensures that if the data is too big for one packet, the adapter knows how to piece the "conversation" together.
These videos explains how the CAN and UDS works:
The Long Answer:
When you request data, like engine oil pressure, into RaceChrono, you use these values:
OBD-II Header: 0x700
PID: 0x221074
It's actually a bit misleading. These values really enables communication with UDS (Unified Diagnostic Services) rather than OBD-II. UDS is a much more powerful system used in modern cars.
Here is how those numbers break down:
0x700: CAN ID, the Engine ECU's "address". This varies by manufacturer.
0x22: The UDS service "Read Data by Identifier."
0x1074: The Data Identifier (DID) for engine oil pressure. This varies by manufacturer.
When engine ECU receives this request it responds with value for oil pressure at that moment.
If DID is different, say 0x1638 it will respond with M/T oil temperature instead.
Why ATCEA2A is needed?
AT CEA 2A is an ELM327 command that sets the CAN Extended Address to 0x2A.
0x750 CAN ID you are using for requesting tire information is the address the Main Body ECU and the 0x2A is extended address for TPMS ECU.
Think of the CAN ID 0x750 as an apartment building and 0x2A as the specific apartment where the TPMS ECU lives. Without the apartment number, your request never reaches the right door.
Why ATTA2A?
AT TA 2A helps manage ISO-TP multi frame responses. Basically, it ensures that if the data is too big for one packet, the adapter knows how to piece the "conversation" together.
These videos explains how the CAN and UDS works:
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