LAUNCH
3001
User’s Manual
18
Exhaust Gas
Sensor Monitor
Once per trip
1
2
1
3 trips
40
PM Filter 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-Trip
DTCs.
When a
Type “A”
DTC is found on the First Trip, the following events take
place:
The computer commands the MIL “On” when the failure is first found.
If the failure causes a severe misfire that may cause damage to the catalytic
converter, the MIL “flashes”
once per second
. The MIL continues to flash as
long as the condition exists. If the condition that caused the MIL to flash is no
longer present, the MIL will light “steady” On.
A DTC is saved in the computer’s memory for later retrieval.
A “Freeze Frame” of the conditions present in the engine or emissions system
when the MIL was ordered “On” is saved in the computer’s memory for later
retrieval. This information shows fuel system status (closed loop or open loop),
engine load, coolant temperature, fuel trim value, MAP vacuum, engine RPM
and DTC priority.
When a
Type “B”
DTC is found on the First Trip, the following events take place:
Summary of Contents for CReader 3001
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