K 2500 Suburban 4WD V8-5.7L VIN R (1999)
System Diagnostics
The system diagnostics are tests that monitor and evaluate a particular emissions system and the effect that system has on vehicle emissions. The system
diagnostics consist of the following:
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The catalyst monitor diagnostic tests.
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The misfire monitor diagnostic tests.
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The fuel trim system diagnostic tests.
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The evaporative emissions (EVAP) system diagnostic tests.
Catalyst Monitor Diagnostic Tests
The emissions control system used on this vehicle has a 3-way catalytic (TWC) converter in order to reduce exhaust emissions of hydrocarbons (HC),
carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst material inside of the converter promotes a chemical reaction in order to combine
oxygen with the HC and CO, converting them to water vapor (H2O) and harmless carbon dioxide (CO2). The NOx is converted to nitrogen (N) by the
converter.
The control module has the ability to monitor the efficiency of the catalytic converter through the use of a heated oxygen sensor (HO2S) mounted in the
engine exhaust gas stream after the catalytic converter (post-catalyst).
Three Way Catalyst (TWC) 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.
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Fuel containing high amounts of the following contaminants:
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Sulfur
