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I have an ELM327-based OBD2 reader that I can issue commands to when connected to a car. I'm running this on a 2015 Acura RDX.

When I issue the request 0100 to get supported mode 1 PIDs, I get the following two responses back:

41 00 98 3A 80 03
41 00 BF BF A8 93

My understanding is that if there are multiple ECUs that can respond to a request they will both answer, so this may be why there are two responses. Does this mean that if I now issue a request that both support, I should get two answers back? And if I issue a request that only one or the other supports, I should only get back one?

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  • Maybe the reader is returning multiple lines of supported PIDs? If you decode the response does it make sense? OBD2 is limited to the engine computer and I would think that when they set up modules they would stay away from multiple responses to the same PID. – Ben Mar 28 '16 at 22:54
  • No, it is from multiple ECUs. This is well known behaviour. What is not clear is what happens when requests are issued that multiple ECUs know how to respond to. – Ana Mar 29 '16 at 8:04
8

try this

AT H1

this will turn on headers, then do

0100

you will get something like 

7E8 06 41 00 BE 3E A8 13
7E9 06 41 00 98 18 80 13

which says you are getting results from ECUs 7E8 (engine) and 7E9 (transmission)

if you are running on an 11bit CAN. If you get 

18 DA F1 18 06 41 00 88 18 00 13
18 DA F1 10 06 41 00 BE 5F A8 13

then its results from ECUs 18DAF110 (engine) and 18DAF118 (transmission) from 29 bit CAN.

If you just want to hear from the engine only then issue

AT CRA 7E8

for 11 bit CAN or 

AT CRA 18DAF110

for 29 bit CAN
dont forget to issue 

AT H0

to turn headers back off

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