Catalyst Efficiency Monitor
The catalyst efficiency monitor is an on-board strategy designed to monitor and determine when a catalytic converter has deteriorated below the minimum level of effectiveness in its ability to control exhaust emissions. This monitor relies mainly on the front and rear oxygen sensors to infer catalyst efficiency based upon oxygen storage capacity. The front and rear oxygen sensor voltages are integrated under specified conditions for the purpose of calculating a rear to front oxygen sensor voltage ratio. After the integrated voltage ratio is calculated, it is compared against a minimum emission threshold value for a healthy catalyst. If the rear-to-front integrated voltage ratio is less than the emission threshold, the catalyst has failed. As catalyst efficiency degrades, its ability to store oxygen declines and it will begin to have a lower rear to front integrated voltage ratio and low HC efficiencies. In general, as catalyst efficiency decreases, the integrated rear-to-front voltage ratio decreases. Inputs from the Engine Coolant Temp (ECT) sensor, Intake Air Temp (IAT) sensor, and Throttle Position (TP) sensors are required to enable the federal test procedure catalyst monitor. To aid in monitor descriptions. refer to illustration. See Figure.
- When the rear-to-front oxygen sensor integrated voltage ratio is too low when compared to the emission threshold value for a deteriorated catalyst, the catalyst test fails. DTCs associated with this test are DTCs P0420, P0421 and P0430.
- The Malfunction Indicator lamp (MIL) is turned on after 3 sequential failures of the Catalyst Efficiency Monitor.