Starting system – general information and precautions
General description
The starting system consists of the starter relay, the starter motor and starter solenoid assembly, the battery, the battery cables, the ignition switch and key lock cylinder, the clutch pedal position switch (manual transmissions), the Transmission Range (TR) sensor (automatic transmissions) and the wiring connecting these components. All starter motors are located on the lower part of the engine, near the transmission bellhousing, where they can engage the ring gear on the flywheel (manual transmissions) or the drive-plate (automatic transmissions).
The starting system has two separate circuits: A low-amperage control circuit, which operates on less than 20 amps, and a high-amperage supply circuit that delivers between 150 and 350 amps to the starter motor (700 amps on diesel engines). The low-amp control circuit includes the ignition switch, the clutch pedal position switch or PNP switch, the starter relay, the coil inside the starter solenoid and the wire harness connecting these components. The high-amp supply circuit consists of the battery, the battery cables, the contact disc in the starter solenoid and the starter motor itself.
On vehicles with a manual transmission, the clutch pedal position switch is installed in series between the ignition switch and the bat tery terminal on the control side of the starter relay coil. The clutch pedal position switch is normally open to prevent the starter relay from being energized when the ignition switch is turned to START unless the clutch pedal is depressed. This setup prevents the starter motor from operating while the clutch disc and the flywheel are engaged. The starter relay coil ground terminal is always grounded.
On vehicles with an automatic transmission, the TR sensor is installed in series between the starter relay ground terminal and ground. The TR sensor is normally open to prevent the starter relay from being energized unless the shift lever is in the NEUTRAL or PARK position. When the ignition switch is turned to START, battery voltage is supplied through the low-amperage control circuit to the battery terminal of the starter relay coil if the shift lever is in the NEUTRAL or PARK position. If it isn’t, the starter circuit remains open and the engine won’t start.
When the starter relay coil is energized, the normally-open relay contacts close and connect the relay common supply terminal to the relay’s normally-open terminal. The closed relay contacts energize the windings of the starter solenoid pull-in coil, which pulls in the solenoid plunger, which pulls the shift lever in the starter motor, which engages the starter’s overrunning clutch and pinion gear with the starter’s ring gear. As the solenoid plunger reaches the end of its travel, the solenoid contact disc completes the high-current starter supply circuit and energizes the solenoid plunger hold-in coil. Current flows from the solenoid battery terminal to the starter motor and energizes the starter.
The starter motors used on the vehicles covered in this manual are not rebuildable because no parts are available. They’re sold as complete new or remanufactured assemblies. If any part of the starter motor fails, including the starter solenoid, the entire assembly must be replaced.
Precautions
Always observe the following precautions when working on the starting system:
a) Excessive cranking of the starter motor can overheat it and cause serious damage. Never operate the starter motor for more than 15 seconds at a time without pausing to allow it to cool for at least two minutes.
b) The starter is connected directly to the battery and could arc or cause a fire if mishandled, overloaded or shorted.
c) Always detach the cable (s) from the negative battery terminal(s) before working on the starting system.