Enabling Conditions (Stage Two)— The follow-
ing conditions must be met to enable the EVAP Mon-
itor (without LDP)
•
Ambient Air Temperature
•
Barometric Pressure
•
Fuel level
•
Engine Temperature
•
Engine run time
•
RPM stable
•
MAP
•
Generator, radiator fans, A/C clutch
Pending Conditions-With or Without LDP—
The EVAP Monitor is suspended and does not run,
when the MIL is illuminated due to any of the fol-
lowing faults:
•
Misfire
•
Oxygen Sensor Monitor
•
Fuel System Rich
•
Fuel System Lean
•
EGR Monitor
•
MAP
•
TPS
•
ECT
•
DCP Solenoid
Conflict Conditions-With or Without LDP—
The EVAP Monitor does not run if any of the follow-
ing tests are in progress:
•
Catalyst
•
EGR
•
Fuel System
•
Misfire
TRIP DEFINITION
OPERATION
A “Trip” means vehicle operation (following an
engine-off period) of duration and driving mode such
that all components and systems are monitored at
least once by the diagnostic system. The monitors
must successfully pass before the PCM can verify
that a previously malfunctioning component is meet-
ing the normal operating conditions of that compo-
nent. For misfire or fuel system malfunction, the
MIL may be extinguished if the fault does not recur
when monitored during three subsequent sequential
driving cycles in which conditions are similar to
those under which the malfunction was first deter-
mined.
Anytime the MIL is illuminated, a DTC is stored.
The DTC can self erase only when the MIL has been
extinguished. Once the MIL is extinguished, the
PCM must pass the diagnostic test for the most
recent DTC for 40 warm-up cycles (80 warm-up
cycles for the Fuel System Monitor and the Misfire
Monitor). A warm-up cycle can best be described by
the following:
•
The engine must be running
•
A rise of 40°F in engine temperature must occur
from the time when the engine was started
•
Engine coolant temperature must reach at least
160°F
•
A “driving cycle” that consists of engine start up
and engine shut off.
Once the above conditions occur, the PCM is con-
sidered to have passed a warm-up cycle. Due to the
conditions required to extinguish the MIL and erase
the DTC, it is most important that after a repair has
been made, all DTC’s be erased and the repair veri-
fied.
MONITORED COMPONENT
DESCRIPTION
There are several components that will affect vehi-
cle emissions if they malfunction. If one of these com-
ponents
malfunctions
the
Malfunction
Indicator
Lamp (Check Engine) will illuminate.
Some of the component monitors are checking for
proper operation of the part. Electrically operated
components now have input (rationality) and output
(functionality) checks. Previously, a component like
the Throttle Position sensor (TPS) was checked by
the PCM for an open or shorted circuit. If one of
these conditions occurred, a DTC was set. Now there
is a check to ensure that the component is working.
This is done by watching for a TPS indication of a
greater or lesser throttle opening than MAP and
engine rpm indicate. In the case of the TPS, if engine
vacuum is high and engine rpm is 1600 or greater
and the TPS indicates a large throttle opening, a
DTC will be set. The same applies to low vacuum
and 1600 rpm.
Any component that has an associated limp in will
set a fault after 1 trip with the malfunction present.
Refer to the Diagnostic Trouble Codes Description
Charts in this section and the appropriate Power-
train Diagnostic Procedure Manual for diagnostic
procedures.
The following is a list of the monitored compo-
nents:
•
Comprehensive Components
•
Oxygen Sensor Monitor
•
Oxygen Sensor Heater Monitor
•
Catalyst Monitor
COMPREHENSIVE COMPONENTS
Along with the major monitors, OBD II requires
that the diagnostic system monitor any component
that could affect emissions levels. In many cases,
these components were being tested under OBD I.
The OBD I requirements focused mainly on testing
25 - 16
EMISSION CONTROL SYSTEMS
NS
DESCRIPTION AND OPERATION (Continued)
