Tracker 2WD L4-1.6L VIN 6 (2000)
Catalytic Converter: Testing and Inspection
Catalyst Monitor Diagnostic Operation
The OBD 2 catalyst monitor diagnostic measures the oxygen storage capacity of the 3-way Catalytic Converter (TWC). Heated oxygen sensors (HO2S)
are installed before (pre-catalyst) and after (post-catalyst) the TWC. Voltage variations between the sensors allow the PCM to determine the performance
of the TWC catalyst. When the TWC catalyst becomes less effective in promoting chemical reactions, the catalyst capacity to store and release oxygen is
generally degraded. The OBD 2 catalyst monitor diagnostic is based on a correlation between the conversion efficiency of the TWC catalyst and the
oxygen storage capacity of the catalyst. A good catalyst, e.g. 95 percent hydrocarbon conversion efficiency, will show a relatively flat output voltage on
the post-catalyst (HO2S 2). A degraded catalyst, 65 percent hydrocarbon conversion, will show greatly increased activity in the output voltage from the
post catalyst HO2S.
The post-catalyst HO2S is used to measure the oxygen storage/release capacity of the catalyst in the TWC. A high oxygen storage capacity indicates a
good catalyst. A low oxygen storage capacity indicates a failing catalyst. The TWC and the HO2S 2 must be at operating temperature in order to achieve
the correct oxygen sensor voltages, like those shown in the post-catalyst HO2S outputs graphic.
The catalyst monitor diagnostic is sensitive to the following conditions:
^
Any exhaust leaks
^
Any HO2S contamination
^
Any alternative fuels
Exhaust system leaks may cause any of the following results:
^
A false failure for a normally functioning or good catalyst.
^
Prevent a degraded or bad catalyst from failing the catalyst monitor diagnostic.
^
Prevent the catalyst monitor diagnostic from running.
The presence of HO2S contaminants may prevent the catalyst monitor diagnostic from functioning properly.
