Diagnostic Trouble Codes (DTCs)
With OBD II, different DTC faults have different priorities according to regulations. As a result, the priorities deter-
mine MIL illumination and DTC erasure. DTCs are entered according to individual priority. DTCs with a higher pri-
ority overwrite lower priority DTCs.
Priorities
Priority 0 —Non-emissions related trouble codes
Priority 1 — One trip failure of a two trip fault for non-fuel system and non-misfire.
Priority 2 — One trip failure of a two trip fault for fuel system (rich/lean)or misfire.
Priority 3 — Two trip failure for a non-fuel system and non-misfire or matured one trip comprehensive com-
ponent fault.
Priority 4 — Two trip failure or matured fault for fuel system (rich/lean) and misfire or one trip catalyst dam-
aging misfire.
Non-emissions related failures have no priority. One trip failures of twotrip faults have low priority. Two trip failures
or matured faults have higher priority. One and two trip failures of fuel system and misfire monitor take precedence
over non-fuel system and non-misfire failures.
DTC Self Erasure
With one trip components or systems,the MIL is illuminated upon test failure and DTCs are stored.
Two trip monitors are components requiring failure in two consecutive trips for MIL illumination. Upon failure of the
first test, the Task Manager enters a maturing code. If the component failsthe test for a second time the code
matures and a DTC is set.
After three good trips the MIL is extinguished and the Task Manager automatically switches the trip counter to a
warm-up cycle counter. DTCs are automatically erased following 40 warm-up cycles if the component does not fail
again.
For misfire and fuel system monitors, the component must pass the test under a Similar Conditions Window in order
to record a good trip. A Similar Conditions Window is when engine RPM is within ±375 RPM and load is within
±10% of when the fault occurred.
NOTE: It is important to understand that a component does not have to fail under a similar window of oper-
ation to mature. It must pass the test under a Similar Conditions Window whenitfailedtorecordaGood
Trip for DTC erasure for misfire and fuel system monitors.
DTCs can be erased anytime with a DRB III. Erasing the DTC with the DRB III erases all OBD II information. The
DRB III automatically displays a warning that erasing the DTC will also erase all OBD II monitor data. This includes
all counter information for warm-up cycles, trips and Freeze Frame.
Trip Indicator
TheTri pis essential for running monitors and extinguishing the MIL. In OBD II terms,atripisasetofvehicle
operating conditions that must be met for a specific monitor to run. All trips begin with a key cycle.
Good Trip
The Good Trip counters are as follows:
Specific Good Trip
Fuel System Good Trip
Misfire Good Trip
Alternate Good Trip (appears as a Global Good Trip on DRB III)
Comprehensive Components
Major Monitor
Warm-Up Cycles
Specific Good Trip
The term Good Trip has different meanings depending on the circumstances:
If the MIL is OFF, a trip is defined as when the Oxygen Sensor Monitor and the Catalyst Monitor have been
completed in the same drive cycle.
EVAPORATIVE EMISSIONS
DESCRIPTION - EVAP SYSTEM
The evaporation control system prevents the emission of fuel tank vapors into the atmosphere. When fuel evapo-
rates in the fuel tank, the vapors pass through vent hoses or tubes into the two charcoal filled evaporative canisters.
The canisters temporarily hold the vapors. The Powertrain Control Module(PCM) allows intake manifold vacuum to
draw vapors into the combustion chambers during certain operating conditions.
All gasoline powered engines use a duty cycle purge system. The PCM controls vapor flow by operating the duty
cycle EVAP purge solenoid. Refer to Duty Cycle EVAP Canister Purge Solenoid for additional information.
When equipped with certain emissions packages, a Leak Detection Pump (LDP) will be used as part of the evap-
orative system. This pump is used as a part of OBD II requirements. Refer to Leak Detection Pump for additional
information. Other emissions packages will use a Natural Vacuum Leak Detection (NVLD) system in place of the
LDP. Refer to NVLD for additional information.
NOTE: The hoses used in this system are specially manufactured. If replacement becomes necessary, it is
important to use only fuel resistant hose.
SPECIFICATIONS
TORQUE
DESCRIPTION Nꞏm Ft. Lbs. In. Lbs.
EVAP Canister Mounting
Nuts11 -95
EVAP Canister Mounting
Bracket-to-Frame Bolts14 10125
Leak Detection Pump
Mounting Bolts11 - 9 5
Breathers (PCV system) 12 - 106
Leak Detection Pump
Filter Mounting Bolt11 - 9 5
