Trips and Drive Cycles
TripA trip is defined as a Key-ON, Key-OFF event in which the Powertrain Control Module (PCM) detects the following:
1. Engine coolant should exceed 70°C (158°F).
2. Engine coolant temperature should change more than 20°C (68°F) after starting the engine.
3. Engine speed should go over 400 rpm.
When the PCM detects an emission related Diagnostic Trouble Code (DTC), it uses the trip information to make its decision on whether to illuminate the Malfunction Indicator Lamp (MIL) light.
Trip Display on Diagnostic Tool
The on-board system readiness function is available on all diagnostic tools. This function indicates the status of each OBD II System Readiness Tests (SRT). One Parameter Identification Display (PID) on a diagnostic tool summarizes the status of all monitors.
Trips and Malfunction Indicator Lamp Function
Trips are used by the software strategy to control the Malfunction Indicator Lamp (MIL) off function. The MIL is turned on after an emission related Diagnostic Trouble Code (DTC) is stored in memory. The MIL is turned off if there are three consecutive drive cycles (refer to Drive Cycle in Diagnostic Methods) without the identical fault under similar conditions or three trips without the identical fault present. The actual number of drive cycles or trips necessary to control the MIL varies with each monitor. (Refer to specific monitor description and operation.)
Trips and Diagnostic Trouble Codes
A Diagnostic Trouble Code (DTC) will be stored in memory after the identical fault has been detected consecutively on at least two separate drive cycles (not necessarily completing a trip). A misfire detection monitor DTC can be stored immediately depending on the misfire type. A catalyst efficiency monitor DTC can be stored after three identical faults are detected on three separate drive cycles. A DTC will be erased from memory after 40 engine warm-up cycles, except for misfire or fuel injection system DTCs which will be cleared after 80 warm-up cycles, if the fault has not been detected after the Malfunction Indicator Lamp (MIL) is turned off. DTC memory storage requirements vary with each monitor. (Refer to the specific monitor for more information.)
Drive Cycle
A drive cycle is a method of driving a vehicle to run all of the on-board diagnostics. It can also be a method of driving a vehicle to initiate and complete a specific OBD II System Readiness Test (SRT) or trip. A drive cycle may be done in the service bay or may require specific drive modes such as a number of idle periods, steady vehicle speed per time, accelerations at certain throttle angles, and others.
OBD II Drive Cycle
The OBD II Drive Cycle is a specific method used to perform all trip monitor tests, as well as the catalyst efficiency monitor test. (Refer to Drive Cycle in Diagnostic Methods.) Diagnostic Strategies
OBD II System Readiness Tests (SRT):
Inspection/Maintenance Testing - OBD II System Readiness Tests
In some areas of the country, it may become a legal requirement to pass an Inspection/Maintenance (I/M) test of the On-Board Diagnostic Generation II (OBD II) system. Before I/M testing can proceed, the OBD II System Readiness Tests (SRT) must all indicate a "yes" condition; if not, the OBD II Drive Cycle must be performed. During the mix of city and highway driving involved in the OBD II drive cycle, the diagnostic monitors will test certain parts of the OBD II software and hardware used to control vehicle emissions. While some of the monitors will run to completion and indicate a Yes or No, others such as misfire or fuel system will continuously run.