Catalytic converter (Mitsubishi Matrix)

The efficiency of the catalytic converter is demonstrated by its ability to oxidize carbon monoxide and hydrocarbons (CH). The engine control unit compares the signals from the front and rear oxygen sensors to determine when the signal voltage from the rear oxygen sensor begins to match the signal voltage from the front sensor. As the catalytic converter wears, the signal waveform from the rear oxygen sensor begins to match the signal waveform from the front sensor, since the converter becomes saturated with oxygen and is no longer able to effectively use oxygen to oxidize hydrocarbons and carbon monoxide into water and carbon dioxide. When the converter is completely worn out, the signals from the front and rear oxygen sensors completely match.

Conditions for storing fault codes

The efficiency of the catalytic converter is determined by comparing the signals from the front and rear oxygen sensors. The ECU stores a fault code and illuminates the engine management system malfunction indicator lamp if the signals from the front and rear sensors in two driving cycles are the same for 60% of the time of two or four 170-second test periods. The test is performed under the following conditions:

• The ECU operates in a closed control loop;
• crankshaft speed within 1800–2300 min⁻¹;
• catalytic converter temperature above 372°C;
• the degree of cyclic opening of the purge solenoid valve of the adsorber is greater than 0.9;
• gear shifting does not occur;
• engine load is within 1.4–4.5 ms.

The output of this code indicates that the signals from the front and rear oxygen sensors have determined that the efficiency of the catalytic converter of the exhaust gases is low.