What data is passed from the ECU to the data port on obd1 hondas? It's not just error codes right? Does anyone know what is passed to the data port when a honda dealer or anyone else with the equipment hooks your car up to a diagnostic machine?

 

obd1 hondas dont have a diagnostic port.
OBD2 only

 

actually some obd1 hondas have a second connector that is a 3 pin connector (94 or 95 civics etc)- it hooks up to the honda pgm tester and can provide low resolution data stream. It can be helpful but reading codes with the MIL and hooking up your meter to the offending components is just as productive. I don't know of any other scanners that can access this with the 3 pin connector- I could be wrong.