Express 1/2 Ton Van V8-5.7L VIN R (1999)
Catalytic Converter: Testing and Inspection
Three Way Catalyst (TWC) Oxygen Storage Capacity
Three-Way Catalyst Oxygen Storage Capacity
The control module monitors the post catalyst HO2S signal voltage in order to measure the oxygen storage capacity of the converter. A good catalytic
converter is indicated when the post-catalyst HO2S signal voltage is relatively steady (2) compared to the pre-catalyst HO2S signal voltage (1).
A malfunctioning catalytic converter is indicated when the post-catalyst HO2S signal voltage is more active (2), similar to the pre-catalyst HO2S signal
voltage (1).
In addition to catalyst monitoring the post catalyst HO2S has a limited role in fuel control.
IMPORTANT: Do not use post-catalyst HO2S voltage activity in order to determine the efficiency of the TWC converter unless directed to do so by a
diagnostic procedure.
The catalyst monitor on-board diagnostic tests can be effected by the following:
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A slightly degraded or marginal catalyst
^
Fuel containing high amounts of the following contaminants:
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Sulfur
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Silica
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Lead
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Phosphorus
^
Exhaust system leaks may cause the following:
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Prevent a degraded or marginal TWC converter from failing a diagnostic test.
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Cause a normally functioning TWC converter to fail a diagnostic test
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Prevent the diagnostic test from running.
^
An aftermarket HO2S.
