Principles of Operation: Notes
The starting system is electronically controlled by the PCM. The PCM receives the following inputs:
- Transmission in PARK or NEUTRAL, from the digital Transmission Range (TR) sensor
- Correctly coded ignition key, from the Passive Anti-Theft System (PATS), vehicles equipped with PATS
- Starter motor request, ignition switch in the START position
- BJB Run/start relay voltage
When the ignition switch is placed in the START position, voltage is supplied to the Body Control Module (BCM) internal logic. A starter motor request signal is also sent to the PCM. If the PCM recognizes the required input signals, it provides the starter relay coil with both voltage and ground. The starter relay contacts close, providing voltage to the starter solenoid, allowing the starter motor to activate. The starter motor continues to crank until the ignition key is released from the START position.
When the starter solenoid is energized, a magnetic field is created in the starter solenoid windings. The iron plunger core is drawn into the starter solenoid coil, and a drive lever and pin connected to the starter drive engages the drive pinion gear to the flywheel ring gear. When the plunger is pulled all the way in, its contact disc closes the circuit between the battery and the motor feed terminals. This sends current to the motor and the drive pinion gear cranks the flywheel to start the engine. When current flows to the starter motor, the starter solenoid pull-in coil is bypassed and the hold-in coil keeps the drive pinion gear engaged with the flywheel.
An overrunning clutch in the starter drive protects the starter motor from excessive speeds, during the brief period before the driver releases the ignition switch from the START position, as the engine starts.
Vehicles equipped with an automatic transmission have a digital TR sensor. The digital TR sensor prevents operation of the starter motor unless the transmission is in NEUTRAL or PARK.