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. 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 P0430, indicating that the three-way catalytic converter's oxygen storage capacity is below a threshold considered acceptable. DTC P0430 is a type A DTC.

The VCM will turn ON the Malfunction Indicator Lamp (MIL).

The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.

Difficulty running the OBD II status DTC P0430 test may be encountered in areas where test conditions cannot be maintained easily, especially in urban areas. To minimize the amount of driving required to complete the test, use the following procedure

Number(s) below refer to the step number(s) on the Diagnostic Table.

2. This table includes checks for conditions that can cause the three-way catalytic converter efficiency to appear degraded. Inspect and repair exhaust system as necessary per Exhaust System. Also inspect the HO2S 2 pigtail and engine harness for any damage that can cause an intermittent fault in HO2S 2 sensor signal HIGH and LOW circuits.

3. If the three-way catalytic converter needs to be replaced, make sure that another condition is not present which caused the catalyst to be damaged. These conditions include a) misfire; b) high engine oil consumption or coolant consumption; c) retarded spark timing or weak spark. To avoid damaging the replacement three-way catalytic converter, correct engine misfire or mechanical fault before replacing three-way catalytic converter.