Starting System: Description and Operation

Starting System

The starting system consists of the following:

- Starter motor
- Starter solenoid
- Starter drive
- Starter motor relay
- Battery
- Digital Transmission Range (TR) sensor (4R75E transmission)
- Ignition switch
- PCM
- Start diode, part of the One-Touch Integrated Start (OTIS) system

The function of the starting system is to crank the engine at a speed fast enough to permit the engine to start. 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 flexplate ring gear. When the plunger is pulled all the way in, the 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 flexplate 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 flexplate.

The 4R75E automatic transmission has a digital TR sensor mounted on the transmission. The TR sensor prevents operation of the starter motor unless NEUTRAL or PARK is selected.

The TorqShift transmission has a Park/Neutral Position (PNP) switch in the transmission. The PNP switch prevents operation of the starter motor unless PARK or NEUTRAL is selected.


One-Touch Integrated Start (OTIS)

The vehicle is equipped with OTIS, a computer-assisted cranking system. This feature assists in starting the engine. If the ignition key is turned to the START position and released when the engine begins cranking, the engine may continue cranking for up to 10 seconds or until the vehicle starts.

Once the ignition is turned to the START position, the PCM reads starter motor request from the ignition switch and gains control of the starter engagement. The customer is no longer in the loop after the initial crank request, the customer may release the key to the RUN position. The PCM will disengage the starter motor based on the following events:

- The engine is started (rpm threshold)
- A set time has been exceeded
- The ignition key has been turned to the OFF position