Powertrain Chart 5, Mil On (No Codes Present)

PCM controls MIL through circuit No. 419. Light will illuminate when PCM detects a problem that will affect vehicle emissions, or cause powertrain damage or driveability problems. MIL will illuminate when certain PCM trouble codes are present or when system is in diagnostic mode.

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

1. With ignition on, MIL should be off. Check if any other fault is present.
2. Check for diagnostic trouble code(s) causing MIL to illuminate.
3. If MIL goes off when PCM connector 3E/3F is disconnected, replace PCM. If MIL stays on, repair circuit No. 419 for a short to ground.

Fig 1: Powertrain Chart 5 Schematic, MIL On (No Codes Present)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Powertrain Chart 5 Diagnostic Flow Chart, MIL On (No Codes Present)

Courtesy of GENERAL MOTORS CORP.