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.
If the MIL is ON and a DTC was set by the Fuel Monitor or Misfire Monitor (both continuous monitors), the
vehicle must be operated in the Similar Condition Window for a specified amount of time.
If the MIL is ON and a DTC was set by a Task Manager commanded once-per-trip monitor (such as the Oxy-
gen Sensor Monitor, Catalyst Monitor, Purge Flow Monitor, Leak DetectionPump Monitor, EGR Monitor or
Oxygen Sensor Heater Monitor), a good trip is when the monitor is passed on the next start-up.
If the MIL is ON and any other emissions DTC was set (not an OBD II monitor), a good trip occurs when the
Oxygen Sensor Monitor and Catalyst Monitor have been completed, or two minutes of engine run time if the
Oxygen Sensor Monitor and Catalyst Monitor have been stopped from running.
Fuel System Good Trip
To count a good trip (three required) and turn off the MIL, the following conditions must occur:
Engine in closed loop
Operating in Similar Conditions Window
Short Term multiplied by Long Term less than threshold
Less than threshold for a predetermined time
If all of the previous criteria are met, the PCM will count a good trip (threerequired) and turn off the MIL.
Misfire Good Trip
If the following conditions are met the PCM will count one good trip (three required) in order to turn off the MIL:
Operating in Similar Condition Window
1000 engine revolutions with no misfire
Warm-Up Cycles
Once the MIL has been extinguished by the Good Trip Counter, the PCM automatically switches to a Warm-Up
CycleCounterthatcanbeviewedontheDRBIII.Warm-UpCyclesareusedtoerase DTCs and Freeze Frames.
Forty Warm-Up cycles must occur in order for the PCM to self-erase a DTC and Freeze Frame. A Warm-Up Cycle
is defined as follows:
Engine coolant temperature must start below and rise above 160° F (71.1°C).
Engine coolant temperature must rise by 40° F (4.4°C)
No further faults occur
Freeze Frame Data Storage
Once a failure occurs, the Task Manager records several engine operating conditions and stores it in a Freeze
Frame. The Freeze Frame is considered one frame of information taken by an on-board data recorder. When a fault
occurs, the PCM stores the input data from various sensors so that technicians can determine under what vehicle
operating conditions the failure occurred.
The data stored in Freeze Frame is usually recorded when a system fails the first time for two trip faults. Freeze
Frame data will only be overwritten by a different fault with a higher priority.
CAUTION: Erasing DTCs, either with the DRB III or by disconnecting the battery, also clears all Freeze
Frame data.
Similar Conditions Window
The Similar Conditions Window displays information about engine operation during a monitor. Absolute MAP (engine
load) and Engine RPM are stored in this window when a failure occurs. There are two different Similar conditions
Windows: Fuel System and Misfire.
FUEL SYSTEM
Fuel System Similar Conditions Window— An indicator that ’Absolute MAP When Fuel Sys Fail’ and ’RPM
When Fuel Sys Failed’ are all in the same range when the failure occurred. Indicated by switching from ’NO’
to ’YES’.
Absolute MAP When Fuel Sys Fail— The stored MAP reading at the time of failure. Informs the user at
what engine load the failure occurred.
Absolute MAP— A live reading of engine load to aid the user in accessing the Similar Conditions Window.
RPM When Fuel Sys Fail— The stored RPM reading at the time of failure. Informs the user at what engine
RPM the failure occurred.
