P0422

Diagram Chart:

CIRCUIT DESCRIPTION

In order to maintain a reasonably low emissions of the Hydrocarbons (HC), the Carbon Monoxide (CO), and the 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. This reaction converts the gases into a harmless water vapor and carbon monoxide. The catalyst also reduces the NOx, converting the gas into nitrogen. The ECM monitors this process via the post catalyst HO2S signal. The post catalyst HO2S, located in the exhaust stream after the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalyst's ability to convert the exhaust emissions effectively. If the catalyst is functioning correctly, the post catalyst HO2S signal will be far less active than that produced by the pre-catalyst HO2S. If the ECM detects an excessive post catalyst signal activity (outside of an acceptable range) for an extended period of time, the ECM will set this DTC. This indicates that the three-way catalytic converter's oxygen storage capacity is below a threshold considered acceptable.

CONDITIONS FOR RUNNING THE DTC

^ P0100, P0110, P0115, P0116, P0120, P0133, P0135, P0141, P0153, P0155, P0161, P0171, P0172, P0174, P0175, P0300 thru P0306, P0440, P0441, P0443, or P0560 not set.

^ The Closed Loop is enabled.

^ The intake air temperature is above -8°C (17.6°F).

^ The calculated TWC temperature is greater than 352°C (666°F).

^ The engine load is between 1.6-3.2 ms.

^ The engine speed is between 1,200 and 2,200 RPM.

CONDITIONS FOR SETTING THE DTC

^ The amplitude ratio (rear HO2S to front HO2S) must be greater than a predetermined value.

^ The above conditions are met for about 5 minutes.

ACTION TAKEN WHEN THE DTC SETS

The ECM illuminates the Malfunction Indicator Lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The ECM turns off the MIL after three consecutive drive trips that the diagnostic runs and does not fail.

^ A History DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other emission related diagnostic.

^ The ECM battery voltage is interrupted.

^ The scan tool clears the MIL/DTC.

TEST DESCRIPTION

The number(s) below refer to the step numbers on the diagnostic table:

4. Before replacing the Three Way Catalytic Converter, make sure that any conditions which may have caused the catalyst to be damaged have been corrected.