Emissions - OBDII I/M Readiness Testing
Information IB05-03-S002I/M Readiness As Part Of Emission Inspection And
Maintenance Program For OBD II Vehicles
ISSUE DATE: OCTOBER 2005
Affected Vehicles
2003-2006 Isuzu Ascender (US/UT)
2003-2006 Isuzu i-280/i-350 (TI)
Service Information
Inspection Maintenance (I/M) program
Several states require that vehicles pass OBD system I/M emissions inspection. These inspections may apply to any 1996 and newer model year OBD II equipped passenger cars and light duty trucks.
As part of an OBD I/M emission inspection, the vehicle's I/M readiness status is checked to ensure that the vehicle's OBD system has properly evaluated the emissions systems of the vehicle for proper operation. To ensure vehicles are capable of passing this portion of the inspection, technicians can review the I/M readiness test status using the I/M System Status display on the Tech 2 and on the Isuzu PowerLink2 Diagnostics. This display provides test data that will verify whether the vehicle's OBD systems have run. States performing inspections on an advisory basis will not reject vehicles for not being I/M-ready.
Conditions for Updating the I/M System Status
Each OBD II system requires at least one diagnostic test. A system monitor is complete when all of the DTCs that report to the system monitor have run and passed or failed. The results of a failed test are reported by a diagnostic trouble code (DTC).
Once all of the tests are complete, the I/M System Status display indicates YES in the "Completed" column. For example, when the H025 Heater Test indicates YES, all oxygen sensor heaters have been diagnosed.
When any required test for a specified system has not run, the "Completed" column under I/M System Status displays NO. The following is a list of conditions that would set the I/M System Status indicator to NO:
^ The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
^ The battery has been disconnected or discharged below operating voltage.
^ The control module power or ground has been interrupted.
^ The control module has been reprogrammed.
^ The control module DTCs have been cleared as part of a service procedure.
Monitored Emission Control Systems
The OBD II System monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with AIR or EGR.
The following is a complete list of the vehicle's systems that may require monitoring by the OBD system:
^ Air conditioning system
^ Catalytic converter efficiency
^ Comprehensive component monitoring (emission-related inputs and outputs)
^ Evaporative Emissions (EVAP) system
^ Exhaust Gas Recirculation (EGR) system
^ Fuel delivery system
^ Heated catalyst monitoring
^ Misfire monitoring
^ Oxygen sensor system (02S or HO2S)
^ Oxygen sensor heater system (HO2S heater)
^ Secondary Air Injection (AIR) system
If a specific vehicle is not required to monitor one or more of the above listed systems, the Tech 2 display will read "not supported." Any non-supported system will not be considered when determining the readiness of the overall system.
For the specific DTCs related to each system, refer to the Service Manual for further diagnostic information on conditions for running the DTC or refer to the publication information mentioned in this bulletin to order the Inspection Maintenance Emissions Diagnostics Manual and follow the I/M Readiness Testing System DTC Tables. Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list. These tests run continuously on some vehicles and may not require an indicator.
Diagnostic Aids
The I/M System Status display indicates when the control module has completed the required tests. This does not necessarily mean that the test has passed, only that a decision was made. If the diagnostic fails, a DTC will indicate the failure. If a failure indication is present, it may prevent other required tests from running. For example, a DTC for the control circuit of the relay controlling an AIR pump may not be listed in the Inspection Maintenance System DTC Table because it is a continuous test. If this DTC is set, the Active Tests for the AIR system may not run and AIR system readiness could display "NO".
The I/M System Status information may be useful for a technician to determine if diagnostics have run when verifying repairs.
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