Catalytic Converter Diagnostic

The three-way catalytic converter stores oxygen found in the exhaust gases and uses it to make reduce toxic gases in the exhaust gases. The catalytic convener is a three-way catalytic converter in which HC (hydrocarbons) and CO (carbon monoxide) are oxidized and NOx (nitrogen oxides) are reduced. As the three-way catalytic converter ages its ability to store oxygen drops. This reduces the conversion capacity of the three-way catalytic converter. To stop conversion capacity becoming too low the engine control module checks three-way catalytic converter efficiency using the two heated oxygen sensors. This check is carried out as follows.

Two heated oxygen sensors are used to check the three-way catalytic converter one upstream and one downstream of the catalytic converter. The main function of the heated oxygen sensors is to measure the oxygen content in the exhaust gases so that the engine control module can maintain the fuel/air mixture at around Lambda = 1. This mixture provides optimum three-way catalytic converter efficiency. To determine catalytic converter efficiency the amplitude of the heated oxygen sensor signals is compared (amplitude is a measure of signal oscillation).

When three-way catalytic converter efficiency is good and the fuel/air mixture is normal, the front heated oxygen sensor signal switches between rich and lean (large amplitude) while the rear heated oxygen sensor signal is even (small amplitude). When three-way catalytic converter efficiency is poor and the fuel/air mixture is normal, the rear heated oxygen sensor signal switches between rich and lean (large amplitude) because the exhaust gases are passing straight through the three-way catalytic converter without being converted

If rear sensor amplitude becomes too great in relation to the front sensor signal for a number of diagnostic tests, diagnostic trouble code EFI-443 Catalytic converter efficiency will be stored.