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Torque » Torque OBD ECU Scanner » Torque Discussion / Ideas » Multiple ECUs Reply - How?

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Author	Topic: Multiple ECUs Reply - How?

extremerotary

Member
Posts: 5

Multiple ECUs Reply - How?
on: March 18, 2024 (GMT)

Good evening,
I recently purchased the torque pro app to help gain some additional understanding of the CAN bus and OBD2 protocols. A friend of mine has a 2009 Hyundai Accent. For kicks, I ran the PID scanner on it and found that multiple ECUs are replying. I’m trying to understand how the app was able to get 2 responses.

For example, the raw reply to 0x20:
e906412080018001
ef0641208007e011

Is this to indicate that 2 modules replied when the app sent just 1 command? Or, did the app make 2 requests; one with a header of 7e906 and one with a header of 7ef06? If the latter, how did it determine the appropriate header to send to each module? I did not see a PID available that I could query to “get module information”. Is there such a thing that I’m just ignorant of? In the PID scanner output, column B for “Header” just says “Default” so I don’t know what that means. Is there a “default” header I should be putting on subsequent requests?Using the ELM327 and some basic code, I manually made a request to 0x20, and I only received 1 response, and it did not have a header. Instead, it was just “41 20 80 01 80 01”.

Hopefully someone can provide me a bit more guidance! Thanks in advance!

cintakc

Member
Posts: 1663

Re: Multiple ECUs Reply - How?
on: March 19, 2024 (GMT)

Does this mean that 2 modules responded when the application only sent 1 command?

Yes, 2 ECUs, an engine block and an automatic transmission unit answered immediately

In the PID scanner output, column B for “Header” just says “Default”

try this for motor enter address 7E7 here

Capp777

Member
Posts: 2994

Re: Multiple ECUs Reply - How?
on: March 19, 2024 (GMT)

Greetings Cintakc.

It has been awhile for me
but wouldn’t that be a 7E1
and 7E7 for the mode 01 pid 20 request.

ATSH may be useful in this case.

7E1

80 01 80 01

1000 0000 0000 0001

7E7

80 07 e0 11

1000 0000 0000 0111

1110 0000 0001 0001

Just curious if this
pid responds for both modules…

0121

Search Wiki for info on
OBD Pids.

extremerotary

Member
Posts: 5

Re: Multiple ECUs Reply - How?
on: March 19, 2024 (GMT)

Thank you both for your replies. Is the header 7E7 and/or 7E1 a “standard” for requesting data specifically from the engine ECU?

In my example above, it looks like the 2 modules that are responding, one started with 7EF and the other with 7E9. I don’t understand how the torque app was able to determine what headers to use in order to address these two modules individually.

Capp777

Member
Posts: 2994

Re: Multiple ECUs Reply - How?
on: March 19, 2024 (GMT)

Search Wiki for OBD-II Pids.

Information is there that
should help.

Interesting reading for me
anyway.

extremerotary

Member
Posts: 5

Re: Multiple ECUs Reply - How?
on: March 20, 2024 (GMT)

I have read them, but either I missed it, or there is no standard for headers. Do you know how to determine which modules are in a vehicle so that I might be able to individually address them?

cintakc

Member
Posts: 1663

Re: Multiple ECUs Reply - How?
on: March 20, 2024 (GMT)

possible options for EKUs addresses

engine: 7DF/7E8, 7E0/7E8, 7E7/7EF
AT: 7E1/7E9

for example (7E7/7EF)
7E7 – request address in the engine ECU
7EF – response address from the engine ECU

extremerotary

Member
Posts: 5

Re: Multiple ECUs Reply - How?
on: March 20, 2024 (GMT)

Okay great, thank you very much for that info. I’ll make some adjustments and test!

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