Adapter<->Vehicle Communication sometimes not successful

[mickeyl]

Sometimes I receive reports where the OBD2 adapter gets recognized successfully, but for some reason the adapter<->vehicle can't negotiate on a common protocol. I wonder whether there's anything we can do about it.

We already try manual protocol selection if the automatic fails – perhaps we should improve the init sequence?

Here is a sample log:

ATD
OK

>ATZ
ATZ


ELM327 v1.5

>ATE0
ATE0
OK

>ATRV
13.9V

>ATSP0
OK

>ATE0
OK

>ATL1
OK



>ATH1
OK



>ATI
ELM327 v1.5



>ATS1
OK



>ATIGN
ON



>0100
SEARCHING...
...UNABLE TO CONNECT



>ATTP1
OK



>0100
NO DATA



>ATTP2
OK



>0100
NO DATA



>ATTP3
OK



>0100
BUS INIT: ...ERROR



>ATTP4
OK



>0100
BUS INIT: ...ERROR



>ATTP5
OK



>0100
BUS INIT: ERROR



>ATTP6
OK



>0100
NO DATA



>ATTP7
OK



>0100
NO DATA



>ATTP8
OK



>0100
NO DATA



>ATTP9
OK



>0100
NO DATA



>

[mickeyl]

Chances are our init sequence is correct, and it's rather a faulty adapter (of which there are literally thousands…).

See also brendan-w/python-OBD#22

It is also possible that most of these issues are due to electrical problems (such as incorrect seating of the adapter in the socket), or missing ignition. It is – unfortunately – impossible to programmatically decide whether ignition is on or off. ATIGN is not doing what it is supposed to. It returns ON as soon as the adapter has power.

[hirurgaa]

@mickeyl I’m currently testing with OBDLink CX and it always returns that ignition is off, where clearly its on- tested with car scanner and etc.

[mlawlerau]

I wonder if we can tell anything from the voltage read via ATRV. Perhaps if the engine is running, we might have a higher voltage? But I guess it doesn't help with detecting the ignition being ON but the engine not running.