Jeep Cherokee

 Service Manual

Starting systems
Description and operation

Starting system

DESCRIPTION

An electrically operated engine starting system is standard factory-installed equipment on this model.

The starting system is designed to provide the vehicle operator with a convenient, efficient and reliable means of cranking and starting the internal combustion engine used to power the vehicle and all of its accessory systems. The starting system includes the following major components:

•  Battery
•  Battery cables
•  Clutch pedal position switch (manual transmission)
•  Ignition switch
•  Park/neutral position switch (automatic transmission)
•  Starter motor (including the integral starter solenoid)
•  Starter relay.

The starting system consists of two separate circuits.

A high-amperage feed circuit that feeds the starter motor between 150 and 350 amperes of battery current, and a low-amperage control circuit that operates on less than 20 amperes of battery current.

The starting system high-amperage feed circuit includes the battery, the battery cables, the contact disc portion of the starter solenoid, and the starter motor. The following starting system feed circuit components are covered in more detail in other areas of this service manual:

•  The battery is located in the passenger side front corner of the engine compartment, near the upper radiator crossmember and provides the electrical current needed to operate the starting system. Refer to Battery in the index of this service manual for the location of more information on the battery.
•  The battery cables connect the battery to the electrical system of the vehicle and to the starting system. Refer to Battery Cables in the index of this service manual for the location of more information on the battery cables.

The starting system low-amperage control circuit includes the ignition switch, the clutch pedal position switch (manual transmission), the park/neutral position switch (automatic transmission), the starter relay, the electromagnetic windings of the starter solenoid, and the wire harnesses that connect these components. The following starting system control circuit components are covered in more detail in other areas of this service manual:

•  The ignition switch is mounted on the bottom of the steering column and actuates the starting system when a properly coded ignition key is inserted in the ignition lock cylinder on the right side of the steering column and turned to the spring-loaded momentary Start position. Refer to Ignition Switch and Key Lock Cylinder in the index of this service manual for the location of more information on the ignition switch.
•  The clutch pedal position switch is integral to the master cylinder of the clutch hydraulic linkage assembly on models equipped with a manual transmission. Refer to Clutch Hydraulic Linkage in the index of this service manual for the location of more information on the clutch pedal position switch.
•  On models with the 2.5L engine, the park/neutral position switch is threaded into the left side of the automatic transmission case and has a springloaded plunger that is actuated by a cam integral to the gearshift mechanism within the transmission. The back up lamp switch is also integral to the park/ neutral position switch. On models with the 4.0L engine, the park/neutral position switch is mounted on the right side of the automatic transmission case. The switch is indexed to and driven by the transmission manual valve shaft. Refer to Park/Neutral Position Switch in the index of this service manual for the location of more information on either version of the park/neutral position switch.

Following are general descriptions of the starter relay and the starter motor. See the owner's manual in the vehicle glove box for more information on the features, use and operation of the starting system.

Refer to Starting System in the index of this service manual for the location of complete wiring diagrams for the starting system.

NOTE: This group covers both Left-Hand Drive (LHD) and Right-Hand Drive (RHD) versions of this model. Whenever required and feasible, the RHD versions of affected vehicle components have been constructed as mirror-image of the LHD versions.

While most of the illustrations used in this group represent only the LHD version, the diagnostic and service procedures outlined can generally be applied to either version. Exceptions to this rule have been clearly identified as LHD or RHD, if a special illustration or procedure is required.

OPERATION

If the vehicle is equipped with a manual transmission, the clutch pedal position switch is installed in series between the ignition switch and the coil battery terminal of the starter relay. This normally open switch prevents the starter relay from being energized when the ignition switch is turned to the momentary Start position, unless the clutch pedal is fully depressed. This feature prevents starter motor operation while the clutch disc and the flywheel are engaged. The starter relay coil ground terminal is always grounded on vehicles with a manual transmission.

If the vehicle is equipped with an automatic transmission, battery voltage is supplied through the lowamperage control circuit to the coil battery terminal of the starter relay when the ignition switch is turned to the momentary Start position. The park/ neutral position switch is installed in series between the starter relay coil ground terminal and ground.

This normally open switch prevents the starter relay from being energized and the starter motor from operating unless the automatic transmission gear selector is in the Neutral or Park positions.

When the starter relay coil windings are energized, the relay directs battery current to the starter solenoid coil windings. When the starter solenoid coil windings are energized, the solenoid directs battery current to the starter motor, which cranks the engine by engaging the starter pinion gear with the starter ring gear. Once the engine starts, the ignition switch key is released by the vehicle operator. When the ignition switch key is released, the switch automatically returns to the On position, which de-energizes the starting system.

Starter motor

DESCRIPTION

Fig. 1 Starter Motors

1 - STARTER SOLENOID

The starter motors used for both the 2.5L and the 4.0L engines available in this model are not interchangeable (Fig. 1). However, each of these starter motors incorporates several of the same features to create a reliable, efficient, compact, lightweight and powerful unit. Both starters feature high torque direct current electric motors. Inside both starter motors the commutator of the rotating motor armature is contacted by four brushes. The starter motor for the 2.5L engine is driven by four permanent magnet field poles, while the starter motor for the 4.0L engine is driven by four electromagnetic field coils wound around four pole shoes. The 2.5L starter motor is rated at 1.2 kilowatts (about 1.6 horsepower) output at 12 volts, while the 4.0L starter motor is rated at 1.4 kilowatts (about 1.9 horsepower) output at 12 volts.

These starter motors are equipped with a planetary gear reduction (intermediate transmission) system.

The planetary gear reduction system consists of a gear that is integral to the output end of the electric motor armature shaft that is in continual engagement with a larger gear that fits on a spline on the input end of the starter pinion gear shaft.

This feature makes it possible to reduce the dimensions of the starter. At the same time, it allows higher armature rotational speed and delivers increased torque through the starter pinion gear.

Both starter motors use an overrunning clutch and starter pinion gear unit to engage and drive the starter ring gear, which is integral to the flywheel (manual transmission) or torque converter drive plate (automatic transmission) mounted on the rear crankshaft flange. Shims are available and can be used to adjust the 2.5L starter motor mounting position to correct for improper starter pinion gear to starter ring gear engagement.

The starter motors for both engines are activated by an integral heavy duty starter solenoid switch mounted to the overrunning clutch housing. This electromechanical switch connects and disconnects the feed of battery current to the starter motor through a movable contact on one end of the solenoid core or plunger. At the same time, the solenoid plunger actuates a shift fork that engages and disengages the starter pinion gear with a starter ring gear. The starter solenoid has two electromagnetic windings or coils, a pull-in coil and a hold-in coil. The pull-in coil requires more battery current and produces a stronger electromagnetic field than the hold-in coil.

Both starter motors are serviced only as a unit with their starter solenoids, and cannot be repaired.

If either component is faulty or damaged, the entire starter motor and starter solenoid unit must be replaced.

OPERATION

When the starter solenoid pull-in coil windings are energized the solenoid plunger is drawn into the electromagnetic coil. The solenoid plunger pulls the shift lever in the starter motor. This engages the starter overrunning clutch and pinion gear with the starter ring gear on the manual transmission flywheel or on the automatic transmission torque converter drive plate. As the solenoid plunger reaches the end of its travel, it moves the solenoid contact disc to complete the high-amperage starter feed circuit and energizes the solenoid hold-in coil windings. Battery current now flows between the solenoid battery terminal and the starter field terminal, energizing the starter and cranking the engine.

Once the engine starts, the overrunning clutch protects the starter motor from damage by allowing the starter pinion gear to spin faster than the pinion shaft. When the solenoid plunger hold-in coil is deenergized, the solenoid plunger return spring returns the plunger to its relaxed position. This causes the solenoid contact disc to open the starter feed circuit, and the shift lever to disengage the overrunning clutch and pinion gear unit from the starter ring gear.

Starter relay

DESCRIPTION

Fig. 2 Starter Relay

The starter relay (Fig. 2) is an electromechanical device that switches battery current to the pull-in coil of the starter solenoid when the ignition switch is turned to the Start position. The starter relay is located in the Power Distribution Center (PDC), in the engine compartment. See the fuse and relay layout label affixed to the inside surface of the PDC cover for starter relay identification and location.

The starter relay is a International Standards Organization (ISO) relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions.

The starter relay cannot be repaired or adjusted and, if faulty or damaged, it must be replaced.

OPERATION

The ISO relay consists of an electromagnetic coil, a resistor or diode, and three (two fixed and one movable) electrical contacts. The movable (common feed) relay contact is held against one of the fixed contacts (normally closed) by spring pressure. When the electromagnetic coil is energized, it draws the movable contact away from the normally closed fixed contact, and holds it against the other (normally open) fixed contact.

When the electromagnetic coil is de-energized, spring pressure returns the movable contact to the normally closed position. The resistor or diode is connected in parallel with the electromagnetic coil in the relay, and helps to dissipate voltage spikes that are produced when the coil is de-energized.