Catalyst diagnostic system and method

A catalytic converter catalyst diagnostic method comprising the steps of:

• (a) measuring a first temperature of an engine exhaust gas flowing into the catalytic converter before the gas enters the catalytic converter catalyst;
• b) measuring a second temperature of the catalytic converter catalyst;
• (c) determining a value indicative of exothermic activity of the catalytic converter responsive to a difference between the first and second temperatures;
• (d) monitoring the difference between the first and second temperatures over a time period;
• (e) enabling use of the value to indicate an operating condition of the catalytic converter only if, during the time period, the difference between the first and second temperatures varies by less than a threshold indicating a change in temperature difference between the first and second temperature sensors.

A catalytic converter catalyst diagnostic method comprising the steps of:

• (a) measuring a first temperature of an engine exhaust gas flowing into the catalytic converter before the gas enters the catalytic converter catalyst;
• (b) measuring a second temperature of the catalytic converter catalyst;
• (c) determining a first value indicative of exothermic activity of the catalytic converter responsive to a difference between the first and second temperatures;
• (d) multiplying the first value by a weighting factor that increases as mass air flow into the engine increases and vise verse;
• and
• (e) updating a second value indicative of an operational status of the catalytic converter responsive to a result of the multiplying step.