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User’s Manual
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more quickly, to bring the vehicle into closed-loop operation as soon as possible.
The Oxygen Sensor Heater Monitor is supported by “spark ignition” vehicles only.
The Oxygen Sensor Heater Monitor is a “Two-Trip” Monitor. If a fault is found on
the first trip, the computer temporarily saves the fault in its memory as a Pending
Code. The computer does not command the MIL on at this time. If the fault is
sensed again on the second trip, the computer commands the MIL “On,” and
saves the code in its long-term memory.
3. Catalyst Monitor
The catalytic converter is a device that is installed downstream of the exhaust
manifold. It helps to oxidize (burn) the unburned fuel (hydrocarbons) and partially
burned fuel (carbon monoxide) left over from the combustion process. To
accomplish this, heat and catalyst materials inside the converter react with the
exhaust gases to burn the remaining fuel. Some materials inside the catalytic
converter also have the ability to store oxygen, and release it as needed to oxidize
hydrocarbons and carbon monoxide. In the process, it reduces vehicle emissions
by converting the polluting gases into carbon dioxide and water.
The computer checks the efficiency of the catalytic converter by monitoring the
oxygen sensors used by the system. One sensor is located before (upstream of)
the converter; the other is located after (downstream of) the converter. If the
catalytic converter loses its ability to store oxygen, the downstream sensor signal
voltage becomes almost the same as the upstream sensor signal. In this case, the
monitor fails the test.
The Catalyst Monitor is supported by “spark ignition” vehicles only. The Catalyst
Monitor is a “Two-Trip” Monitor. If a fault is found on the first trip, the computer
temporarily saves the fault in its memory as a Pending Code. The computer does
not command the MIL on at this time. If the fault is sensed again on the second
trip, the computer commands the MIL “On” and saves the code in its long-term
memory.
4. Heated Catalyst Monitor
Operation of the “heated” catalytic converter is similar to the catalytic converter.
The main difference is that a heater is added to bring the catalytic converter to its
operating temperature more quickly. This helps reduce emissions by reducing the
converter’s down time when the engine is cold. The Heated Catalyst Monitor
performs the same diagnostic tests as the catalyst Monitor, and also tests the
catalytic converter’s heater for proper operation.
The Heated Catalyst Monitor is supported by “spark ignition” vehicles only. This
Monitor is also a “Two-Trip” Monitor.
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