Catalyst Monitor
BACKGROUNDCurrent vehicles use a three-way catalytic converter to reduce emission of harmful gases. The converters are referred to as three-way because they specifically address three pollutants (hydrocarbons, carbon monoxide, and nitrogen oxide) produced in the combustion chamber. The catalyst monitor uses a pair of inputs to indirectly measure how effective the catalyst is at reducing emissions.
OPERATION
O2 sensors located above (upstream) and below (downstream) the catalytic converter are able to monitor the efficiency of the converter. The dual O2 sensor strategy is based on the fact that. as a catalyst deteriorates, its oxygen storage capacity and efficiency are both reduced. By monitoring the oxygen storage capacity of the catalyst, its efficiency can be indirectly calculated. The upstream sensor detects the amount of oxygen in the exhaust gas before it enters the converter. This sensor should switch fairly rapidly.
A functioning converter stores oxygen so that it can be used for the oxidation of hydrocarbons (HC) and carbon monoxide (CO). The downstream sensor detects a lower oxygen level in the exhaust than does the upstream sensor. It indicates this by switching at a significantly slower rate than does the upstream sensor.
As the converter deteriorates and loses its ability to store oxygen, the switch rate at the downstream oxygen sensor approaches that of the upstream sensor. The system is monitored so that when the switch rate of the downstream sensor reaches 90% of the switch rate of the upstream sensor (automatic transmissions), the MIL is illuminated. The threshold for manual transmissions is 70%. At this point, exhaust emissions are projected to exceed the legal limit.
ENABLING CONDITIONS
The following conditions must be met before the catalyst monitor will run:
^ Engine coolant temperature greater than 170° F
^ Vehicle speed greater than 20 MPH for 2 minutes
^ Open throttle
^ Closed loop operation
^ RPM between 1,248 and 1,952 (auto), or between 1,248 and 2,400 (manual)
^ MAP voltage between 1.50 and 2.60
PENDING
The catalyst monitor does not run if the MIL is illuminated due to one of the following:
^ Misfire DTC
^ O2 monitor DTC
^ Upstream O2 heater DTC
^ Downstream O2 heater DTC
^ Fuel system rich DTC
^ Fuel system lean DTC
^ Vehicle is on the limp-in mode due to MAP, TPS, or engine temperature DTC
^ Upstream O2 sensor rationality DTC
^ Downstream O2 sensor rationality DTC
CONFLICT
The monitor does not run if any of the following are present:
^ EGR monitor is in progress
^ Fuel system rich intrusive test is in progress
^ Purge monitor is in progress
^ Time since start is less than 60 seconds
^ One trip misfire maturing code
^ One trip O2 monitor maturing code
^ One trip upstream O2 heater maturing code
^ One trip downstream O2 heater maturing code
^ One trip fuel system rich maturing code
^ One trip fuel system lean maturing code
SUSPEND
Results of the monitor are not recorded until the O2 monitor passes.
Catalyst efficiency is monitored once each trip. The MIL is illuminated and a DTC stored if the switch rate of the downstream O2 sensor reaches 90% of the upstream sensor's switch rate for vehicles equipped with an automatic transmission and 70% for vehicles equipped with a manual transmission for a total of two consecutive trips. The message on the scan tool screen appears as follows:
Catalytic Converter Efficiency Failure
Flash Code 64 J 2012 Code P 0422
The MIL is extinguished if the monitor can pass a tougher criteria (downstream sensor switch rate at less than 80% of upstream sensor for automatic transmissions and 60% for manual transmissions) for three consecutive trips. The DTC remains in memory until the monitor has passed this higher criterion for a total of 40 warm-up cycles with no failures.
This malfunction could possibly be caused by problems with any of the following components:
^ Catalytic converter
^ Exhaust manifold (leaks)
^ Wiring harness/connectors
^ PCM
^ O2 sensor
The fault trees in the Diagnostic Procedures book can help you isolate the source of the problem.
NOTE: If the MIL were illuminated by a failed catalytic converter or O2 sensor, engine problems may have been the cause of the failure. If fuel, coolant, or oil are passed through the exhaust, catalyst, or O2 sensor, contamination may result. Before the vehicle is returned to the customer, inspect for the following:
^ Worn engine piston rings
^ Worn engine cylinder head valves and/or guides
^ Leaking head gasket
^ Cracked cylinder head
^ Fuel contamination and quality