Refer to

Cell 21: Oxygen Sensors

In order to maintain a reasonably low emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), the engine controls system uses a three-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and Carbon Dioxide. The catalyst also reduces NOx, converting it to Nitrogen. The PCM monitors this process using Bank 2 HO2S #2. Bank 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 determines the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the Bank 2 HO2S #2 signal will be far less active than that produced by Bank 2 HO2S #1. This indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.

When the conditions for running this DTC are met the following occurs:

1. The PCM captures the current rear HO2S rich/lean status.
2. The Air Fuel ratio transitions from rich to lean or lean to rich depending on the capture rear HO2S rich/lean status.
3. The Air Fuel ratio transitions a second time opposite the first Air Fuel ratio transition.
4. The PCM captures the response time (the time the HO2S goes from below 300 mV to above 600 mV and from 600 mV to below 300 mV) of the front and rear Heated Oxygen sensors when the Air Fuel ratio transitions occurred.
5. The PCM measures the time it takes the rear HO2S voltage to cross a reference rich/lean threshold minus the time it takes the front HO2S voltage to cross the same rich/lean threshold. The time difference from the front and rear HO2S is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold.

The PCM determines the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

The numbers 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.