Users Manual Part 2

38
MDMAXLITEA
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 NO
2
molecules in
the exhaust stream. In some implementations, injection of a
reactant before the aftertreatment purges it. NO
2
in particular
is unstable, and will join with hydrocarbons to produce
H
2
O and N
2
. The NOx Aftertreatment Monitor monitors the
function of the NOx aftertreatment to ensure that tailpipe
emissions remain within acceptable limits.
The NOx Aftertreatment Monitor is supported by
“compression ignition” vehicles only. The NOx Aftertreatment
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.
10. Boost Pressure System Monitor