Description & Operation

When ignition switch is turned to START position, battery voltage is applied to Powertrain Control Module (PCM) ignition crank sense circuit. PCM verifies that shift lever is in Park or Neutral. PCM then grounds control circuit of starter relay. When starter relay is energized, it completes battery voltage circuit to starter solenoid "S" terminal.

When voltage is applied to solenoid windings, this creates movement of solenoid plunger and shift lever, causing drive pinion to engage flywheel and close solenoid switch contacts. See Fig 1 . When solenoid switch contacts close, starter motor energizes and cranks engine. As engine starts, pinion overrun clutch protects armature from excessive speed until ignition switch is opened and plunger return spring disengages pinion. Starter motor is non-repairable, and must be replaced as a unit.

Fig 1: Typical Cranking Circuit Illustration

Courtesy of GENERAL MOTORS CORP.