Starting System: Description and Operation

STARTING SYSTEM

The starting system consists of the:
- starter motor.
- starter switch, part of the ignition switch.
- digital transmission range (DTR) sensor (automatic transmission-equipped vehicles).
- starter motor relay.
- starter solenoid.
- starter drive.

Starter Motor
The starter motor:
- is a wound field, gear reduction, 12V DC motor.
- has an integral starter solenoid.
- has an overrunning clutch in the starter drive.

It functions as follows:
- When the key cylinder turns to the START position, current flows through the solenoid pull-in and hold-in coils until the solenoid plunger is at the end of its travel. The plunger pulls the lever, which pushes the pinion to engage with the flywheel.
- The contact bridges the solenoid terminals that bypass the pull-in coil. This allows the hold-coil to keep the starter drive engaged and to pass battery current to the starter motor. The starter motor cranks the engine fast enough to start it.
- As the key returns to the RUN position, the relay cuts off current to the solenoid. The solenoid disengages the pinion from the flywheel.

Starter Relay
The starter interrupt relay consists of:
- pull-in coil and contacts.

When the key cylinder is in the START position:
- the pull-in coil is activated and pulls the contacts together.
- current passes through the starter relay from the engine compartment power distribution box to the starter solenoid.

When the key cylinder is returned to the RUN position:
- the relay turns off the starter solenoid which disengages the pinion from the flywheel.

Transmission Range Sensor (Automatic Transmission)
The transmission range sensor:
- prevents starter motor engagement unless the transmission is in NEUTRAL or PARK position. Refer to Transmission Control Systems.

Starter Drive
The starter drive:
- is operated by the starter solenoid.
- engages the flywheel to turn the engine.
- has an internal overrunning clutch to disengage the starter motor when the engine starts.

Starter Solenoid
The starter solenoid:
- is an electromagnet.
- engages the starter drive to the flywheel.
- when energized, contacts close, connecting the battery to the starter motor to turn the starter drive.
- is kept in the energized condition by a hold-in winding until the ignition switch is released.