Circuit Description

A three-way catalytic converter is used to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). Catalyst inside converter promotes a chemical reaction which oxidizes HC and CO in exhaust gas, converting them into water vapor and carbon dioxide. Catalyst also reduces NOx converting it to nitrogen. PCM monitors this process using Bank 1 HO2S No. 1 and Bank 1 HO2S No. 2. Bank 1 HO2S No. 1 produces an output signal which indicates amount of oxygen present in exhaust gas entering three-way catalytic converter. Bank 1 HO2S No. 2 produces an output signal that indicates oxygen storage capacity of catalyst, which in turn indicates catalyst's ability to convert exhaust gases efficiently. If three-way catalyst is working efficiently, Bank 1 HO2S No. 1 will be much more active than Bank 1 HO2S No. 2. If Bank 1 HO2S No. 2 signal voltage remains between 400 and 500 millivolts for an extended period of time, DTC P0140 is set. HO2Ss are used to minimize amount of time needed for closed loop fuel control operation and to allow accurate catalyst monitoring. HO2S greatly decrease time required for fuel control sensors Bank 1 HO2S No. 1 and Bank 2 HO2S 1 to become active. HO2Ss are required by post-catalyst monitor sensors to maintain sufficiently high temperature for accurate exhaust/oxygen content readings further from engine.

When DTC sets, PCM illuminates MIL on second trip after fault was detected. PCM will store conditions present when DTC was set as freeze frame data in the FAILURE RECORDS data.

PCM will turn MIL off on third consecutive trip cycle during which diagnostic runs and fault is no longer recognized. A history DTC P0140 will clear after 40 consecutive trip cycles during which diagnostic runs and fault is no longer recognized. DTC can be cleared with scan tool, or by disconnecting battery voltage feed to PCM.