Catalyst Monitor Enabling and Malfunction Criteria

There is no point in trying to monitor catalyst efficiency until both the engine and the catalyst have warmed up and the engine is operating in a steady state. A complete test may take as long as 60 seconds to complete after all the enabling criteria have been met as it requires calculating the average values of 50 samples of the rate of change in amplitude of the post-catalyst sensor.

Once it has begun, the test will be aborted if any of the Evaluation Criteria move out of range. The test will restart as soon as all the Catalyst Warm-up Criteria have been met again.

The complete catalyst monitoring criteria can be broken down as follows:

Preliminary Condition
(In order to begin the test sequence)

^ The diagnostic test must not have been completed (either passed or failed) yet this trip.

Catalyst Warm-up
(Prepares the catalyst for testing)

^ Speed > 0
^ Open Throttle
^ RPM x Load > 60,000
^ Time accelerating > 15 seconds
^ Time at idle < 40 seconds
^ Total fuel cut-off time (decel) < 10 seconds
^ Above conditions fulfilled for 120 seconds





Catalyst Evaluation
(Operating conditions while actively testing)

^ Speed between 30-100 kph
^ Open throttle
^ System operating in closed loop
^ RPM x Load = 60,000-260,000
^ Coolant > 60°C
^ The post-catalyst oxygen sensor has been > 0.4V once during this driving cycle

If you count them, you will find that there are 14 criteria for this one diagnostic. As if that isn't enough, they must also occur in the proper sequence which is why it is critical to always carefully follow the road test instructions for each particular diagnostic.

The road test procedure for catalyst evaluation is to:

^ Erase DTCs
^ Drive the vehicle under varying load and RPM until coolant temperature reaches 60°C, however you must drive at least 5 minutes even if you start with a hot engine.
^ Drive with a constant throttle opening at 40-90 km/h for four minutes, select a gear which will allow you to drive at 2-3,000 RPM.
^ Choose a test route which will allow you to avoid changes in throttle setting. When traffic permits, it is better to let the speed change a bit rather then moving the throttle.
^ Connect Intellegant Saab Tester (ISAT) and read ON/OFF, DIAGNOSIS STATUS, CATALYST. If ISAT rads "READY" then select READ FAULT CODES to see if the repair has been successful.