The service manual (on pages 14-76 and 14-77) has a list of 14 "Diagnosis item"s with corresponding wave forms. I now read (with a scope) a regular square wave that represents "Normal state" (item 14).

Is this all that the ECU reports, or is there a way to get additional codes, maybe by establishing a 2-way dialog with the ECU? I have found lists of error codes of the form Pnnnn but they appear to be for newer models and/or don't apply to this model (ie: turbo, automatic transmission, etc...)

If this is all that the ECU is aware of, I can be confident that the dealer won't find anything else with their expensive testing equipment, otherwise, how can I get to the other error codes, if any?

Does anyone know more details on how to talk to the ECU, or have I done all that can be done?

Thanks.