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Professional 909 User Manual
• It supplies the catalytic converter with the oxygen it needs to oxidize the
carbon monoxide and hydrocarbons left over from the combustion process
during engine warmup.
• The extra oxygen injected into the exhaust stream also helps the catalytic
converter reach operating temperature more quickly during warm-up periods.
The catalytic converter must heat to operating temperature to work properly.
The Secondary Air System Monitor checks for component integrity and system
operation, and tests for faults in the system. The computer runs this Monitor
once per trip.
The Secondary Air System Monitor is a “Two-Trip” monitor. If a fault is found
on the first trip, the computer temporarily saves this 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.
Note: The following Monitors became standard beginning in 2010. The
majority of vehicles produced before this time will not support these Monitors.
8. NMHC (Non-Methane Hydrocarbon Catalyst) Monitor
The non-methane hydrocarbon catalyst is a type of catalytic converter. It helps
to remove non-methane hydrocarbons (NMH) left over from the combustion
process from the exhaust stream. To accomplish this, heat and catalyst materials
react with the exhaust gases to convert NMH to less harmful compounds. The
computer checks the efficiency of the catalyst by monitoring the quantity of NMH
in the exhaust stream. The monitor also verifies that sufficient temperature is
present to aid in particulate matter (PM) filter regeneration.
The NMHC Monitor is supported by “compression ignition” vehicles only. The
NMHC 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.
9. NOx Adsorber Monitor
NOx aftertreatment is based on a catalytic converter support that has been
coated with a special washcoat containing zeolites. NOx Aftertreatment is
designed to reduce oxides of nitrogen emitted in the exhaust stream. The
zeolite acts as a molecular “sponge” to trap the NO and NO2 molecules in
the exhaust stream. In some implementations, injection of a reactant before
the aftertreatment purges it. NO2 in particular is unstable, and will join with
