Circuit Description

WARNING: This page is about a different car, the 2002 Isuzu Rodeo Sport and 2002 Isuzu Rodeo. However, it is still accessible from the selected car via links, so may be relevant.

A three-way catalytic converter is used to control hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) emissions. 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 HO2S-1 and HO2S-2. HO2S-1 produces an output signal which indicates amount of oxygen present in exhaust gas entering three-way catalytic converter. HO2S-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, HO2S-1 will be much more active than HO2S-2. If PCM detects a level of HO2S-2 activity that indicates catalyst in no longer operating efficiently, DTC P0420 will set.

When DTC sets, PCM illuminates MIL as soon as 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 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.