It is not that the codes are wrong, I'd say it is more like the descriptions are not intuitive. The standard codes and the parameter that set them are determined by the SAE, not the individual automakers.
Yeah, you know, with all the infamous Toyota/Lexus idle air control valve failures (so much that Toyota gave out free valves but charged labor -- an arm and a leg), in all cases the ECUs didn't set the P0505 code like it's supposed to.
A P0505 would be set if there was an open or short in the idle air control valve circuit. The ECU has no way of knowing if the IAC is gummed up or not moving enough.
The primary purpose of the OBD II system is to identify if a system that will affect emissions is malfunctioning. Two common misconception are that the OBD II system identify every problem with a vehicle, including ones that affect driveability, and that the component named in the diagnostic trouble code description must be bad if the code names the component. Unfortunately, those misconceptions lead people who may be familiar with older automotive systems but who have not studied the principles behind automotive on board diagnostic systems to give misguided advice.
I've cleaned other manufactorer's IAC without a short circuit that was gummed up and set P0505 like it's supposed to. I guess some ECUs are not as smart as others in being able to checking engine RPMs changes while commanding IACs.
I guess not!
No, that's not correct. Some manufacturers measure P0420 with oxygen store test and some with pre/post sensor waveform test. Conditions under which tests are run can vary greatly between manufacturers.
I think we're discussing a difference in semantics. Yes, the conditions under which tests are run can vary greatly between manufacturers, however, the code number, description, and parameters are set by the SAE. For P0420, the **parameter** that sets the code is a bad catalytic converter, and as you pointed out, there is more than one way to determine whether the parameter is met or not.
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