For 1990-2009 cars

The starters on the Medium Duty are non-repairable starter motors. It has pole pieces that are arranged around the armature within the starter housing. When the solenoid windings are energized, the pull-in winding circuit is completed to ground through the starter motor. The hold-in winding circuit is completed to ground through the solenoid. The windings work together magnetically to pull in and hold in the plunger. The plunger moves the shift lever. This action causes the starter drive assembly to rotate on the armature shaft spline as it engages with the flywheel ring gear on the engine. At the same time, the plunger closes the solenoid switch contacts in the starter solenoid. Full battery voltage is then applied directly to the starter motor and it cranks the engine.

As soon as the solenoid switch contacts close, current stops flowing thorough the pull-in winding as battery voltage is now applied to both ends of the windings. The hold-in winding remains energized; its magnetic field is strong enough to hold the plunger, shift lever, starter drive assembly, and solenoid switch contacts in place to continue cranking the engine. When the engine starts, the pinion gear overrun sprag protects the armature from excessive speed until the switch is opened.

When the ignition switch is released from the CRANK position, voltage is removed from the starter solenoid S terminal. Current flows from the motor contacts through both windings to ground at the end of the hold-in winding. However, the direction of the current flow through the pull-in winding is now in the opposite direction of the current flow when the winding was first energized.

The magnetic fields of the pull-in and hold-in windings now oppose one another. This action of the windings, along with the help of the return spring, cause the starter drive assembly to disengage and the solenoid switch contacts to open simultaneously. As soon as the contacts open, the starter motor is turned off.

### Circuit Description (ECM/PCM Controlled Start)

Moving the ignition switch to the START position sends 12V signal through STRTR fuse supplying 12 V to the starter relay coil. The 12V signal also goes to the Clutch Pedal Switch is on a manual transmission or the Park/Neutral Position Switch on an automatic transmission.When the clutch pedal is depressed or the PNP switch is in the Park/Neutral position the 12V signal will notify the engine control module ECM / powertrain control module (PCM) that CRANK has been requested. The ECM/PCM will then ground the control circuit of the starter relay. The starter relay switch circuit will then close and allow B+ to flow to the starter S terminal, allowing the engine to crank.