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From what I know from the ELM327: OBD to RS232 document , using multi-line responses, it is possible to receive up to 6 PIDs. I would like to know how it's possible for scan tools to receive over a dozen PIDs at once.

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You can request up to 6 PIDs simultaneously from the main controller. The ECU will response to it in multi-frame. here I have answered about mutli frame for MCP2515 chip but it might be the same for any other chips like ELM327 and etc. since it is the CAN protocol, only context might be different.

Answer of your question is YES you can but not only in one request. Many logger devices consider 1 Hz as a minimum requesting time for safely recording all OBD data and below 1 Hz might work or not.

You should at first request the Mode 1 PID 00 which will response in one message and it contains all the PIDs that ECU supports for OBD in bitwise order. How to parse this message is defined in this wikipedia link: Here.

Now you have all the supported PIDs and now you can request them in group of 6 PIDs. This is how any scan tool or OBD loggers are working.

regards,

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mohsen_og
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  • Thanks for the response. So you're saying that using the same request ID, I would have to sent a request for 6 PIDs, then within another time frame, send 6 different PIDs with the same request ID? Was also wondering if you knew an answer to another question I posted here https://stackoverflow.com/questions/42320827/is-it-possible-to-request-all-desired-odb-ii-pids-via-a-dbc-file – SE Student Feb 22 '17 at 19:34
  • @SEStudent with 7DF you can request up to 6 PIDs simultaneously. This means that ECU will response to it if your PIDs are in the supported region. It would take around 20 to 100 ms to receive all the responses (It depends on your code and ECU). Then you send another request with another 6 PIDs and goes on. Then you should make a loop to do it over per second (for example) so you can take the data in 1 Hz. I dont know if you know how to get multiple responses from ECU which would be tricky as well. You should work with First Frame, FlowControl. Here I answered the multiple PID request which ... – mohsen_og Feb 23 '17 at 06:59
  • @SEStudent which I did it for VIN. It will be the same for multiple PIDs as well. http://stackoverflow.com/a/38891041/6072457 – mohsen_og Feb 23 '17 at 07:00