Inspection/Maintenance (I/M) System Check
Inspection/Maintenance (I/M) System CheckDESCRIPTION
Several states require that a vehicle pass on-board diagnostic (OBD) system tests and pass the I/M emission inspection in order to renew the license plates. This is accomplished by viewing the I/M System Status display on a scan tool. Using a scan tool, the technician can observe the I/M System Status in order to verify that the vehicle meets the criteria that comply with the local area requirements.
CONDITIONS FOR UPDATING THE I/M SYSTEM STATUS
Each system requires at least one, and sometimes several, diagnostic tests. The results of these tests are reported by a diagnostic trouble code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have run and passed, or when any one of the DTCs comprising the monitor have illuminated the MIL. Once all of the tests are completed, the I/M System Status display will indicate YES in the Completed column. For example, when the heated oxygen sensor (HO2S) Heater Test indicates YES, all of the oxygen sensor heaters have been diagnosed. If the vehicle has 4 HO2S, all 4 heater circuits have been diagnosed. The I/M System Status will indicate NO under the Completed column when any of the required tests for that system have not run.
The following is a list of conditions that will 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 the 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 secondary air injection (AIR) or exhaust gas recirculation (EGR).
The OBD II regulations require monitoring of the following:
- The air conditioning system
- The catalytic converter efficiency
- Comprehensive component monitoring of the emission-related inputs and outputs
- The evaporative emissions (EVAP) system
- The exhaust gas recirculation (EGR) system
- The fuel delivery system
- Heated catalyst monitoring
- Misfire monitoring
- The oxygen sensor system (O2S or HO2S)
- The oxygen sensor heater system (HO2S heater)
- The secondary air injection (AIR) system
For the specific DTCs required for each system, refer to Inspection/Maintenance (I/M) System DTC Table. Systems such as the fuel delivery, the misfire, and the comprehensive components may not be listed in a system status list. These tests run continuously on some vehicles, and may not require an indicator. Inspection/Maitenance (I/M) System (DTC) Table
DIAGNOSTIC AIDS
The I/M System Status display provides an indication of 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 for a DTC associated with one of the I/M regulated systems, the failure 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 the DTC is a continuous test. If this DTC is set, the Active Tests for the AIR system may not run.
The I/M System Status information may be useful for a technician to determine if diagnostics have run when verifying repairs.
TEST DESCRIPTION
Steps 1-3:
The numbers below refer to the step numbers on the diagnostic table.
1. Any DTCs that set, even DTCs that are not listed in the Inspection/Maintenance System DTC Table, may prevent the required DTCs from running. If there is any question as to whether a set DTC is disabling the required I/M diagnostic, review the Conditions for Running in the diagnostic procedures for the DTC that is required by the I/M diagnostic. A list of disabling DTCs, if applicable, is in the supporting text for that DTC.
2. When a control module is reprogrammed or when the diagnostic trouble codes are cleared as part of a repair procedure, all the I/M System Status indicators will reset to NO.
3. Use discretion when determining whether the entire system set procedure needs to be performed. For example, if the only tests that have not run are tests that require the engine to be at operating temperature, then only those individual tests need to be run. There is no need to allow the engine to completely cool in order to run these tests.