P0420

Diagnostic Chart:

Schematic:

A three-way catalytic converter is used in order to control exhaust emissions of Hydrocarbons (HC), Carbon Monoxide (CO) and Oxides Of Nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes HC and CO that is present in exhaust gas. This will convert HC and CO into a harmless water vapor and a carbon dioxide, and reduces NOx into nitrogen. The catalytic converter also has ability to store oxygen. The PCM has capability to monitor this process by using a Heated Oxygen Sensor (HO2S) which is in exhaust stream past three-way catalytic converter. The HO2S Sensor 2 produces an output signal which indicates oxygen storage capacity of catalyst. This in turn indicates catalyst's ability to convert exhaust emissions effectively. The PCM monitors catalyst efficiency by first allowing catalyst to heat up, waiting for a stabilization period while engine is idling. Then, PCM adds and removes fuel while monitoring reaction of HO2S Sensor 2. When catalyst is functioning properly, HO2S Sensor 2 response to extra fuel is slow compared to O2S 1. When the HO2S Sensor 2 response is close to that of O2S 1, oxygen storage capability or efficiency of catalyst is considered to be bad and MIL will illuminate.

DTC PARAMETERS
^ DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0141, P0171, P0172, P0201 - P0204, P0300, P0325, P0336, P0340, P0341, P0440, P0442, P0446, P0452, P0453, P0480, P0481, P0502, P0503, P0506, P0507, P0563, P0601, P0602, P1133, P1137, P1138, P1441 and P1621 are not set.
^ The engine has been running longer than 520 seconds after the throttle has moved.
^ The BARO is above 72 kPa.
^ Calculated air flow is less than 8 g/sec.
^ Idle time is less than 45 seconds.
^ Battery voltage is greater than 9 volts.
^ Engine speed is greater than 1000 rpm for at least 35 seconds since end of last idle period.

Then, with the vehicle stopped:
^ Idle speed is less than 150 rpm above or less than 75 rpm below the desired idle.
^ The vehicle speed is less than 5 kph (3 mph).
^ The Engine Coolant Temperature (ECT) is above 70°C (158°F) and below 125°C (257°F).
^ The Intake Air Temperature (IAT) is above -20°C (-4°F) and less than 80°C (176°F).
^ The calculated catalytic converter temperature is above 501°C (934°F) and less than 627°C (1161°C). (In order to obtain correct temperature to run test, drive vehicle until converter temperature is 50°C (122°F) above condition for running DTC.)

The above conditions are present for up to 30 seconds and the HO2S Sensor 2 response is too quick.

DIAGNOSTIC AIDS
The catalyst test may abort due to a change in engine load. Do not change engine load (i.e. A/C, coolant fan, blower motor) while a catalyst test is in progress.