Powertrain Chart 4, Mil Inoperative

PCM controls Malfunction Indicator Light (MIL) through circuit No. 419. Light is on when PCM has detected a problem that will affect vehicle emissions, or may cause powertrain damage or driveability problems.

MIL will illuminate when certain PCM trouble code(s) are present or when system is in diagnostic mode.

MIL light will not illuminate when ignition is on and engine is not running, or when engine is running and no PCM code are current. Some codes are stored without activating MIL light.

1. Checks if MIL circuit is okay and if PCM is unable to control output.
2. Checks circuit No. 419 for an open circuit.
3. Checks for open in circuit No. 39 or inside IPC.

Fig 1: Powertrain Chart 4 Schematic, MIL Inoperative

Courtesy of GENERAL MOTORS CORP.

Fig 2: Powertrain Chart 4 Diagnostic Flow Chart, MIL Inoperative

Courtesy of GENERAL MOTORS CORP.