Express 1/2 Ton Van V8-5.7L VIN R (1999)
Oxygen Sensor: Description and Operation
HO2S 2 (Catalyst Monitor)
In order to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx), a three-way catalytic converter is used.
The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless
water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The VCM has the capability to monitor this process using
HO2S 2. HO2S 2, located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage
capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust emissions effectively. A problem with the HO2S 2 electrical circuits
should set DTC P0137, P0138 or P0140, depending on the specific condition. If the catalyst is functioning correctly, the HO2S 2 signal will be far less
active than that produced by HO2S 1. If a problem exists which causes the VCM to detect excessive HO2S 2 activity outside of an acceptable range for
an extended period of time, the VCM will set DTC P0420, indicating that the three-way catalytic converter's oxygen storage capacity is below a
threshold considered acceptable.
