Field Service Mode

If the diagnostic terminal is grounded with the engine running, the system will enter the Field Service Mode. In this mode, the malfunction indicator lamp (MIL) will indicate whether the system is in Open Loop or Closed Loop.

In Open Loop the malfunction indicator lamp (MIL) flashes two and one-half times per second.

In Closed Loop, the lamp flashes once per second. Also, in Closed Loop, the telltale lamp will stay Off most of the time if the system is running lean. It will stay On most of the time if the system is running rich.

While the system is in the Field Service Mode and the Closed Loop timer is bypassed, new trouble diagnostic trouble codes cannot be stored, but information flags can be stored in the PCM.