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Professional 909X User Manual
Misfire Monitor
(Type 2)
Continuous
1
1
1
3 - similar
conditions
80
Fuel System
Monitor
Continuous
1
1 or 2
1
3 - similar
conditions
80
Catalytic
Converter
Monitor
Once per trip
1
2
1
3 trips
40
O
2
Sensor
Monitor
Once per trip
1
2
1
3 trips
40
O
2
Sensor
Heater Monitor Once per trip
1
2
1
3 trips
40
EGR Monitor
Once per trip
1
2
1
3 trips
40
EVAP system
Monitor
Once per trip
1
2
1
3 trips
40
Secondary Air
System
Monitor
Once per trip
1
2
1
3 trips
40
2.7 DTCs and MIL Status
When the vehicle’s on-board computer detects a failure in an emissions-related
component or system, the computer’s internal diagnostic program assigns a
diagnostic trouble code (DTC) that points to the system (and subsystem) where
the fault was found. The diagnostic program saves the code in the computer’s
memory. It records a “Freeze Frame” of conditions present when the fault was
found, and lights the Malfunction Indicator Lamp (MIL). Some faults require
detection for two trips in a row before the MIL is turned on.
Note: The “Malfunction Indicator Lamp” (MIL) is the accepted term used
to describe the lamp on the dashboard that lights to warn the driver that an
emissions-related fault has been found. Some manufacturers may still call
this lamp a “Check Engine” or “Service Engine Soon” light.
There are two types of DTCs used for emissions-related faults: Type “A” and
Type “B.” Type “A” codes are “One-Trip” codes; Type “B” DTCs are usually Two-
