Circuit Description

There should always be a steady Malfunction Indicator Light (MIL) when ignition switch is in RUN position, engine not running. System voltage is applied to the indicator bulb and Powertrain Control Module (PCM) provides a path to ground. Once engine starts, PCM turns the MIL OFF. When an engine control system malfunction occurs, PCM turns ON the MIL and a diagnostic trouble code is stored in memory.