Circuit Description

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 engine control module (ECM) has the ability to monitor this process using the Bank 1 HO2S1 and the Bank 1 HO2S2 heated oxygen sensors. The Bank 1 HO2S2 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three -way catalytic converter. The Bank 1 HO2S2 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust gases efficiently. If catalyst is operating efficiently, the Bank 1 HO2S1 signal will be far more active than that produced by the Bank 1 HO2S2 sensor. If the Bank 1 HO2S2 signal voltage remains between 400mV and 520mV for an extended period of time during the decel fuel cut off mode, DTC P0140 will be set. The oxygen sensor heater greatly decreases the amount of time required for fuel control sensors Bank 1 HO2S1 and Bank 2 HO2S1 to become active. Oxygen sensor heaters are required by post-catalyst monitor sensors to maintain a sufficiently high temperature for accurate exhaust oxygen content readings further from the engine.