Powertrain Chart 4 - Service Engine Soon Light Inoperative

PCM controls SERVICE ENGINE SOON light 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.

SERVICE ENGINE SOON light will glow when certain PCM trouble code(s) are present or when system is in diagnostic mode.

SERVICE ENGINE SOON light will not glow 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 SERVICE ENGINE SOON light.

1. Checks if SERVICE ENGINE SOON light circuit is okay and PCM is unable to control output.
2. This test checks circuit No. 419 for open.
3. Checks for an open in circuit No. 39 or inside PCM.

Fig 1: POWERTRAIN Chart 4 Schematic - SES Light Inoperative

Courtesy of GENERAL MOTORS CORP.

Fig 2: POWERTRAIN Chart 4 Flow Chart - SES Light Inoperative

Courtesy of GENERAL MOTORS CORP.