Diagnostic Instructions
Description
Several states require that a vehicle pass on-board diagnostic (OBD) system
tests and the inspection/maintenance (I/M) emission inspection in order to renew 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 monitor requires at least one, and sometimes several diagnostic
tests. The result of each test is reported by a DTC. A system monitor is complete
when either all of the DTCs composing the monitor have Run and Passed, or when any
one of the DTCs comprising the monitor has illuminated the malfunction indicator lamp
(MIL). Once the system monitor is complete, the I/M System Status display will indicate
YES in the Completed column.
For example, when the HO2S Heater Status indicates YES, either all of the oxygen
sensor heater tests have passed or one of the tests has illuminated the MIL. If the
vehicle has 4 heated oxygen sensors, either all 4 heater circuit tests have passed
or one of the heater circuit tests has illuminated the MIL. 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 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. |
Monitored Emission Control Systems
The OBD II System monitors all emission control systems that are on-board.
The OBD II regulations require monitoring of the following:
| • | The air conditioning system |
| • | The catalytic converter efficiency |
| • | Comprehensive component monitoring--Emission related inputs and outputs |
| • | The evaporative emission (EVAP) system |
| • | The fuel delivery system |
| • | Heated catalyst monitoring |
| • | The oxygen sensor system (O2S or HO2S) |
| • | The oxygen sensor heater system (HO2S heater) |
For the specific DTCs required for each system, refer to
Inspection/Maintenance (I/M) System DTC Table. Systems such as fuel delivery,
misfire, and comprehensive components may not be listed in a system status list. These
tests run continuously and do not require an I/M System Status indicator.
Circuit/System Verification
Review the I/M System Status indicators. All I/M System Status indicators should
report YES.
Circuit/System Testing
Important: Many DTC related repairs will instruct the
technician to clear the DTC information. Clearing the DTC will reset the I/M System
Status indicators to NO. Performing the I/M Complete System Set Procedure will set
each of the I/M System Status indicators to YES.
- Observe the Engine DTC information with a scan tool.
- Review applicable service bulletins for software updates that would prevent
the I/M System Status tests from completing.
- Observe the I/M System Status indicators.
