Description & Operation

WARNING: Vehicles are equipped with air bag supplemental restraint system. Before attempting any repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in appropriate AIR BAG RESTRAINT SYSTEMS article in ACCESSORIES & EQUIPMENT.

CAUTION: When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery.

When ignition switch is turned to START position, battery voltage is applied to Park/Neutral Position (PNP) switch. Current passes through PNP switch only when in transmission is in Park or Neutral. Current flows from PNP switch to coil-side of theft deterrent relay and then to Powertrain Control Module (PCM) where it is grounded to activate theft deterrent relay. PCM grounds start enable circuit when ignition switch is in START position and all theft criteria is met. Battery voltage is also supplied to switch side of theft deterrent relay and then on to starter solenoid when theft deterrent relay is activated.

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 the engine. As engine starts, pinion overrun clutch protects armature from excessive speed until ignition switch is opened and plunger return spring disengages pinion.

Fig 1: Typical Cranking Circuit

Courtesy of GENERAL MOTORS CORP.