Jeep Cherokee (XJ): Transmission ranges and shift lever positions. Transmission control module (TCM). Hydraulic system

Transmission ranges and shift lever positions

The AW-4 transmission has six ranges and shift lever positions. Park, Reverse and Neutral are conventional and mechanically operated. The 1-2, 3 and D ranges provide electronically controlled shifting.

The 1-2 position provides first and second gear only. The 3 position provides first, second and third gear.

The D range provides first through fourth gear.

Overdrive fourth gear range is available only when the shift lever is in D position (Fig. 35).

Fig. 35 AW-4 Shift Lever Positions And Transmission Ranges

Transmission control module (TCM)

DESCRIPTION

The module determines shift and converter clutch engagement timing based on signals from sensors.

The valve body solenoids are activated, or deactivated accordingly.

The TCM has a self diagnostic program. Component and circuitry malfunctions can be diagnosed with the DRB scan tool. Once a malfunction is noted and stored in control module memory, it is retained even after the problem has been corrected. To cancel a stored malfunction, disconnect and reconnect the "Trans." fuse in the module harness.

SENSORS

Sensors include:

•  throttle position sensor (TPS)
•  transmission speed sensor
•  vehicle speed sensor
•  park/neutral position switch
•  brake switch

OPERATION

The throttle position sensor is mounted on the throttle body. It electronically determines throttle position and relays this information to the transmission control module to determine shift points and converter clutch engagement.

The transmission speed sensor consists of a rotor and magnet on the transmission output shaft and a switch in the extension housing or adapter. The sensor switch is activated each time the rotor and magnet complete one revolution. Sensor signals are sent to the transmission control module.

The park/neutral position switch is mounted on the valve body manual shaft. The switch signals shift linkage and manual valve position to the transmission control module through an interconnecting harness.

The switch prevents engine starting in all gears other than Park or Neutral.

The brake switch is in circuit with the torque converter clutch solenoid. The switch disengages the converter clutch whenever the brakes are applied.

The switch is mounted on the brake pedal bracket and signals the transmission control module when the pedal is pressed or released.

Hydraulic system

DESCRIPTION

The hydraulic system consists of the pump, valve body and solenoids, and four hydraulic accumulators.

The oil pump provides lubrication and operating pressure.

The valve body controls application of the clutches, brakes, second coast band, and the converter clutch.

The valve body solenoids control sequencing of the 1-2, 2-3 and 3-4 shift valves. The solenoids are activated by signals from the transmission control module.

The accumulators are used in the clutch and brake feed circuits to control initial apply pressure. Spring loaded accumulator pistons modulate the initial surge of apply pressure for smooth engagement.