Catalyst Efficiency Monitor

DESCRIPTION
The Catalyst Efficiency Monitor is a self-test strategy within the Powertrain Control Module (PCM) that determines when a catalyst has fallen below the minimum level of effectiveness in its ability to control exhaust emissions.



OPERATION
In the Catalyst Efficiency Monitor test, closed loop fuel control is transferred from the front Heated Oxygen Sensor (HO2S) to the downstream HO2S(s). Calculations are made within the monitor strategy to determine the actual output frequency of the downstream HO2S(s). The actual output frequency calculated is called the test frequency. The test frequency is an indication of the oxygen storage capacity of the catalyst. If the test frequency is relatively slow, then the oxygen storage capacity of the catalyst is high. If the test frequency is slow, this is an indication that work is being done within the catalytic converter.

A second frequency called the calibrated frequency is found using the engine RPM and load. The calibrated frequency serves as a high limit for the Catalyst Efficiency Monitor test frequency calculated earlier. The calibrated frequency can be thought of as the lowest acceptable oxygen storage capacity of the catalyst under the given engine RPM and load. If the test frequency is less than the calibrated frequency, the catalyst passes the Catalyst Efficiency Monitor test. Otherwise, the catalyst (or a system/component used by the catalyst monitor) is malfunctioning.


Malfunction Indicator Lamp (MIL) and Diagnostic Trouble Codes (DTC's)
If the strategy detects three consecutive malfunctions on separate drive cycles, a Catalyst Efficiency Monitor DTC is stored in the PCM memory and the MIL is turned on. Once the Catalyst Efficiency Monitor DTC has been stored in the PCM memory, the MIL will be illuminated as long as the malfunction is present. The MIL is turned off after three trips without the malfunction. The Catalyst Efficiency Monitor DTC will be erased after 40 warm-up cycles without the malfunction after the MIL is turned off.

COMPONENTS
The components which make up the Catalyst Efficiency Monitor are the downstream HO2S(s) and the catalyst(s).