How to Understand Trouble Codes

2. Non-Continuous Component Monitor

The Non-Continuous Component Monitors can vary between vehicle engine management systems, but there are several that are common to most vehicles. The term "non-continuous" means that the system and components are checked only under specific operating conditions. Some of the monitoring will occur only once a day. For example, in very hot climates, like those in Arizona and New Mexico, the needed cold start conditions will not be attained for an entire summer, so "stone-cold" startup monitoring will not occur at all during that time.

The Oxygen Heater Monitor is common to all OBD II vehicles. This a multi-factored current/amperage flow test of the heating element common to all modern oxygen sensors and Air Fuel Ratio sensors—AFR is a highly responsive type of oxygen sensor common on most low emission vehicles (LEVs). Usually, as the vehicle is cranked, the Oxygen Heater Monitor checks the vehicle's system voltage. If it is within spec, then soon after startup or the next shut down, the OBD II system will run a series of tests on the heater elements of the vehicle's oxygen sensors. If this monitor passes, then many of the other non-continuous monitors will run. If this monitor fails, then most of the other non-continuous monitoring will be suspended or ignored. Accurate oxygen sensor performance is vital to proper engine emissions management.

The Oxygen Sensor Monitor is common to all ODB II vehicles. After the Oxygen Heater element passes its monitor, the Oxygen Monitor begins to look for the proper conditions to be run. There are a few common conditions that are required on all vehicles in order for the Oxygen Sensor Monitor to run. First, there must not be any misfire codes. Misfire conditions cause erratic oxygen exhaust content, so it is not possible for the monitor to run any accurate oxygen sensor tests. There must not be any fuel trim codes or any excessively lean or rich compensation percentages. This too will skew the oxygen sensor tests, so fuel trim issues will suspend the Oxygen Sensor Monitor.

If the above basic criteria are met, the ODB II system will begin running oxygen sensor tests under a variety of conditions. Some of the most common operating conditions are hard acceleration, highway cruise speed, prolonged idle that is at least 60 seconds, and others depending on the type of vehicle in question and the number of oxygen sensors on board. Some high performance vehicles have a front oxygen sensor for each cylinder and a rear oxygen sensor for the rear of each Catalytic Converter, meaning that some vehicles have up to and above sixteen oxygen sensors.
Since the Catalyst Monitor needs to be sure that the oxygen sensors are reading the exhaust gas oxygen content accurately, the Catalyst Monitor runs after all the oxygen monitors have run. The Catalyst Monitor is testing the ability of the CAT to store oxygen in its Cerium bed. The purpose of the Cerium is to optimize the efficiency of all the sections of the Catalytic Converter.

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