Catalytic Converter Diagnosis (On the Road)

The purpose of the catalytic converter diagnosis is to detect a malfunction that would cause the OBD threshold for HC pollutant emissions to be exceeded.

The catalytic converter's oxygen storage capacity is the indicator of its condition. As the catalytic converter ages, its oxygen storage capacity decreases, along with its ability to treat polluting gases.

I - ENTRY CONDITIONS FOR DIAGNOSIS

The catalytic converter diagnosis can only be carried out after an engine operating time of approximately 16.5 minutes, if the preliminary conditions for switching on the ignition are met and maintained:

• no electrical fault,
• no misfire detected,
• no catalytic converter diagnosis since the ignition was switched on,
• adaptations carried out,
• main loop and dual loop active,
• coolant temperature above 75 °C,
• engine speed read on the diagnostic tool between 1472 rpm and 3868 rpm.

II - FAULT DETECTION

The diagnosis is carried out while driving at a stabilised steady speed.

When the entry conditions for diagnosis are met, rich-lean excitation pulses are applied, which causes bursts of oxygen to be sent into the catalytic converter.

1 - If the catalytic converter is good

It absorbs oxygen and the downstream oxygen sensor PR099 voltage remains at an average value.

2 - If it is worn

It releases oxygen and the downstream oxygen sensor PR099 starts to switch. The oxygen sensor voltage oscillates (the OBD warning lamp lights after three drive cycles).

At the end of this test, it is essential not to switch off the ignition before reading the result on the diagnostic tool.

Switching off the ignition at any point will lead to an incorrect interpretation of the results.

III - CONFIRMING THE REPAIR

If, after the test, the diagnostic tool has recorded catalytic converter fault DF110: "CATALYST", refer to the diagnostic procedure associated with this symptom.