Does anyone know what the iso 9141 L-line is for? It says (otpional) and isn't in the obduino diagram, but I am wondering if it is optional from a vehicle manufacturers perspective as I see it connected on other obd products. I'm looking at a "couple transisters" ISO 9141 add on for a guino so will look into iso 9141 a bit more.
Per here for initialization :
Second article for Evaluation Engineering
The tester sends 51 at 5 baud on both the K- and L-lines. Once completed, the L-line is disabled and idles in the high state.
The vehicle computer(s) wake up, but only the computer responsible for diagnostics answers with 85 at 10.4 kb/s. This is the synchronization byte.
All subsequent communications occur at 10.4 kb/s.
The vehicle computer sends Keyword #1, a 1-byte value.
The vehicle computer sends Keyword #2, a 1-byte value.
Keywords are sent seven data bits with one odd parity bit.
The tester acknowledges by sending the logic bit-wise inversion of Keyword #2.
The vehicle computer acknowledges by sending the logic bit-wise inversion of the wake-up address (that the tester sent in step 1).
At this point, the communications link is initialized and operational.
Once the link is initialized, it must be maintained. If there is no message traffic on the link for 5 s, each computer assumes communications are over. The initialization sequence must be repeated to re-establish the link. The tester may periodically transmit a keep-alive message to maintain the link.