^^
If I recall properly, the actual catalytic converter design on OBD 1 and OBD II are not that different. The difference is not in the converter but in the computer controls monitoring the converter. On OBD II, the ECU is able to detect a failure in a converter and throw on a CEL whereas with OBD I, a failed converter will not be detected. It works as follows:
- On OBD I, the oxygen sensors are placed only before the converter in the exhaust system. It functions to adjust the A/F mixture based on reading the exhaust output.
- On OBD II, it still has the front sensors which are necessary for all computer controlled Fuel Injected cars but in addition to the front sensors, there are also O2 sensors behind the converter. The backend O2 sensors are not used to adjust the A/F like on the front. It compares the "filtered" exhaust air to the pre converter "filtration/gas conversion" reading per the frontend O2 to see if the reading has changed significantly. If it has, the converter is working properly. If the readings on the front and back 02 sensor are similar, this indicates the converter isn't properly converting exhaust gases into less harmful ones and puts on the CEL for converter failure.
Technical issues aside, another change enacted by the new CA requirements is that you can no longer select a converter based on the vehicle size. You have to follow a specific application chart for each car. I'm not sure what criteria has been used in determining the appropriate app.
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