Clearing Trouble Codes

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

When 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 PCM/ECM's memory.

The MIL operates differently on OBD II compliant vehicles. OBD II guidelines require that 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 MIL if test fails or emissions exceed FTP by 1-1/2 times.

If vehicle is experiencing a misfire malfunction that may cause damage to Three-Way Catalytic Converter (TWC), MIL will flash once per-second. Flashing of MIL will continue until vehicle is out of engine speed and load conditions that could cause possible catalyst damage. The MIL will remain illuminated after flashing stops.

When MIL is on, Diagnostic Executive will turn off MIL after three consecutive trips in which a "test passed" has been reported for diagnostic test that originally caused MIL to illuminate. For fuel trim or misfire DTCs, tests must also pass during same operating conditions that DTC is set under (within 375 rpm, within 10% of engine load) and similar engine temperature when DTC set.

DTCs should be cleared after repairs have been completed. Some diagnostic tables will tell you to clear codes before using chart. This allows PCM/ECM to set DTC while going through chart, which will help to find cause of problem more quickly.