$01$00 Erratic responses

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skudd
Posts: 3
Joined: Fri Jan 31, 2014 11:47 pm
cars: 2009 Lancer GTS
2002 Honda Accord EX

$01$00 Erratic responses

Post by skudd »

Greetings!

I know this is primarily a GM community, but it seems like y'all have a better grasp of things OBD-II than most everywhere else I've been around the web.

The case I'm working on right now is with my 2009 Lancer GTS and an ELM327 USB dongle that I have. I've written some simple python code to work with the ELM, and I thought I had a fairly robust setup that would grab the supported mode $01 PIDs and verify against the processed list before requesting another mode $01 PID. What's odd though is that when I tried to grab PID $0C after parsing $00, $20, and $40, my app said that $0C wasn't supported. I knew this was wrong and commented out the validation bit and tried again, and sure enough, I got the data back that I was expecting.

This lead me to try another experiment: in a loop, grab $01$00 repeatedly and print the result. The outcome? It seems to waver between 2 different responses erratically.

Is this a common issue? If so, is there a better way to get the supported PIDs than hitting every 32nd PID in mode $01?
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antus
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Re: $01$00 Erratic responses

Post by antus »

It sounds like buggy ecu code to me. You could handle it like torque on android.. list the pids you could support and put a * next to the ones the ecu claims it supports but allow the user to pick any so if they know a pid is supported and the list is wrong they can still select it.

Or in your case, maybe try and read if each pid is supported 2 or 3 times and if any of them say yes, treat it as a yes.

I dont think that behavior from the pcm willl be something your likely to see on other cars.
Have you read the FAQ? For lots of information and links to significant threads see here: http://pcmhacking.net/forums/viewtopic.php?f=7&t=1396
skudd
Posts: 3
Joined: Fri Jan 31, 2014 11:47 pm
cars: 2009 Lancer GTS
2002 Honda Accord EX

Re: $01$00 Erratic responses

Post by skudd »

Yeah, that's what I was thinking about. The other thing I considered was to just do a sweep of all standard mode $01 PIDs a couple of times then base the support on whether or not they respond with anything. Both seem kinda hack-ish, but I guess that's what it takes here. :-/

Thanks for the feedback!
skudd
Posts: 3
Joined: Fri Jan 31, 2014 11:47 pm
cars: 2009 Lancer GTS
2002 Honda Accord EX

Re: $01$00 Erratic responses

Post by skudd »

Just wanted to share what I've found while sitting in my car right now:

Code: Select all

Enter an OBD-II command: atz
atz: > ELM327 v1.3a
Enter an OBD-II command: atdp
atdp: > AUTO
Enter an OBD-II command: 01 00
01 00: > 41 00 BE 3F B8 13 41 00 88 18 00 13 
Enter an OBD-II command: 01 00
01 00: > 41 00 BE 3F B8 13 41 00 88 18 00 13 
Enter an OBD-II command: 01 00
01 00: > 41 00 BE 3F B8 13 41 00 88 18 00 13 
Enter an OBD-II command: 01 00
01 00: > 41 00 88 18 00 13 41 00 BE 3F B8 13 
Enter an OBD-II command:
Same thing happens for $01$20:

Code: Select all

Enter an OBD-II command: 01 20
01 20: > 41 20 80 17 E0 01 41 20 80 01 80 01 
Enter an OBD-II command: 01 20
01 20: > 41 20 80 01 80 01 41 20 80 17 E0 01 
Enter an OBD-II command: 01 20
01 20: > 41 20 80 17 E0 01 41 20 80 01 80 01 
Enter an OBD-II command: 
This is really annoying. :rant:
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