[obdgpslogger] ELM327 interface "hanging" with NO DATA condition after a random amount of time (Toyota Corolla)

[Gary Briggs]

On Sun, Sep 18, 2011 at 09:33:24PM +0200, Maciej Grela wrote:
> Hi,
> 
> I've been trying out obdgpslogger today with an ELM327 cable connected
> to a Toyota Corolla and I noticed strange behaviour - after a while of
> logging using obdgpslogger the interface "locks up" and the tool can
> no longer receive data from the OBD-II bus. In the output it looks
> like this:
> 
> temp=86.000000
> rpm=1100.000000
> vss=17.000000
> maf=8.720000
> throttlepos=2.745098
> temp=86.000000
> >BD reported NO DATA for 01 0C: NO DATA
> Ending current trip
> >BD reported NO DATA for 01 05: NO DATA
> >BD reported NO DATA for 01 05: NO DATA
> >BD reported NO DATA for 01 05: NO DATA
> >BD reported NO DATA for 01 05: NO DATA
> 
> <...>
> >BD reported NO DATA for 01 05: NO DATA
> >BD reported NO DATA for 01 05: NO DATA
> >BD reported NO DATA for 01 05: NO DATA
> >BD reported NO DATA for 01 05: NO DATA
> >BD reported NO DATA for 01 05: NO DATA
> >BD reported NO DATA for 01 05: NO DATA
> >COBD reported NO DATA for 01 05: NO DATA
> 
> The funny thing is that it seems to be the chip hanging. If you stop
> the logger and restart again it resumes without any problems:
> 
> kraken ~ # obdgpslogger --spam-stdout --serial /dev/ttyUSB0
> --samplerate 10 --db ./obdgpslogger7.db
> Opening serial port /dev/ttyUSB0, this can take a while
> Successfully connected to serial port. Will log obd data
> temp=87.000000
> rpm=1185.000000
> vss=18.000000
> maf=8.690000
> 
> This happens at a random time after startup of obdgpslogger, sometimes
> it's 2 minutes and sometimes it can run for an hour.

If I were a betting man, I'd guess you just have a flakey chip.
Disappointing, but possible. Do you have a brand name device, or was it
something from ebay just labelled "ELM327" ?

Have you seen it happen? When it happens, is there a long pause, or do
the errors start coming back immediately?

Could you turn on serial logging, and see if there's anything of
interest in the logfile at the instant things go south?

> One additional thing I've noticed, is that when this happens the "RX"
> led on the OBD side of my interface stops blinking - as if the ECU
> stopped responding. This may very well be the case but why it
> "unfreezes" when I restart the obdgpslogger ? Is there some special
> command sequence sent to the ECU "resetting" the interface when
> obdgpslogger starts ? Or is this a buggy ELM327 clone ?

Yeah, there's actually a couple. The one that's really causing the reset
is "ATZ", which quietly covers all manner of sins. It's the closest
thing you can get to a power cycle on those chips without an actual
power cycle.

You don't want to insert that into the stream whenever things go south,
because that also resets a bunch of other stuff I do [turn off echo,
turn off spaces, all kinda of performance- and reliability- enhancing
stuff].

I don't really have a good answer, just some general thoughts. I'm
interested to see more though

Gary (-;