Warning About Clearing Trouble Codes

NOTE: To prevent powertrain control module (PCM)/engine control module (PCM/ECM) damage, the key must be OFF when disconnecting or reconnecting the power to the PCM/ECM (for example battery cable, PCM/ECM pigtail connector, PCM/ECM fuse, jumper cables, etc.).

When the PCM/ECM sets a diagnostic trouble code (DTC), Malfunction Indicator Lamp (MIL) will be turned on only for type A and B, and a DTC will be stored in the PCM/ECM's memory.
The Malfunction Indicator Lamp (MIL) operates differently on OBD II compliant vehicles. OBD II guidelines require that the MIL (CHECK ENGINE or SERVICE ENGINE SOON) illuminate only for DTCs that will impact vehicle emissions (type A and B). The Diagnostic Executive will turn on the MIL if the test fails or the emissions exceed the FTP by 1-1/2 times.
If the vehicle is experiencing a misfire malfunction that may cause damage to the Three-Way Catalytic Converter (TWC), the MIL will flash once per second.Flashing of the MIL will continue until the vehicle is out of engine speed and load conditions that could cause possible catalyst damage. The MIL will remain illuminated after flashing stops.
When the MIL is on, the Diagnostic Executive will turn off the MIL after three consecutive trips in which a "test passed" has been reported for the diagnostic test that originally caused the MIL to illuminate. For fuel trim or misfire DTCs, the tests must also pass during the same operating conditions that the DTC was set under (within 375 rpm, within 10% of the engine load and similar engine temperature when the DTC set).
DTCs should be cleared after repairs have been completed. Some diagnostic tables will tell you to clear the codes before using the chart. This allows the PCM/ECM to set the DTC while going through the chart, which will help to find the cause of the problem more quickly.