Land Rover Discovery: Valve Block

The valve block is located in a vertical position at the front of the transmission main casing, behind a sealed cover. The valve block contains a number of solenoids and spool valves to control the transmission operation.

The solenoids are controlled by the TCM to provide gear changes and smooth transition between ratio changes.

If the TCM or the valve block is replaced, a diagnostic routine using an approved Land Rover diagnostic system will be required to calibrate the TCM.

Valve Block Assembly

1. Automatic Transmission Fluid (ATF) pump intake
2. ATF pump pressure outlet
3. Sensor unit
4. System Pressure Control Valve (PCV)
5. Torque converter lock-up clutch PCV
6. Multiplate clutch 'B' PCV
7. Multiplate clutch 'E' PCV
8. Dog clutch A solenoid valve
9. Dog clutch F solenoid valve
10. Multiplate clutch 'D' PCV
11. Multiplate clutch 'C' PCV
12. Park lock solenoid valve
13. Magnetic valve control solenoid - park lock actuator
14. Electrical connector
15. Valve block

Valve Block Components

1. System pressure spool valve
2. Torque converter pressure spool valve
3. Lubrication spool valve
4. Dog clutch 'A' spool valve
5. Dog clutch 'F' spool valve
6. Multiplate clutch 'D' spool valve
7. Magnetic holding valve piston
8. Multiplate clutch 'C' spool valve
9. Park lock spool valve
10. Magnetic valve control solenoid - park lock actuator
11. Park lock solenoid valve
12. Multiplate clutch 'D' Pressure Control Valve (PCV)
13. Multiplate clutch 'C' PCV
14. Retainer
15. Dog clutch 'F' solenoid valve
16. Dog clutch 'A' solenoid valve
17. Multiplate clutch 'E' PCV
18. Multiplate clutch 'B' PCV
19. Torque converter lock-up clutch PCV
20. System PCV
21. Valve housing
22. Intermediate plate
23. Valve and spring
24. Valve and spring
25. Valve and spring
26. Ball rocker
27. Valve and spring
28. Multiplate clutch 'C' spool valve
29. Multiplate clutch 'D' spool valve
30. Pressure sensor
31. Torque converter lock-up clutch spool valve
32. Shift system pressure spool valve
33. Pressure reduction spool valve
34. Valve plate

Pressure Control valves

Six PCV's are located in the valve block. The solenoid operated PCV's are controlled by PWM (pulse width modulation) signals from the TCM. The solenoids convert the electrical signals into hydraulic control pressure proportional to the signal to actuate the spool valves and clutches for precise transmission operation.

Five PCV solenoids for the multiplate clutch and the torque converter lockup clutch supply a higher control pressure as the signal current increases and can be identified by an orange connector cap. The TCM operates the solenoids using PWM signals. The TCM monitors engine load and clutch slip and varies the solenoid duty cycle accordingly. The solenoids have a 12 V operating voltage and a pressure range of 0 - 4.7 bar (0 - 68 lbf.in²).

One PCV solenoid for the system pressure control supplies a lower control pressure as the signal amperage increases and can be identified by a gray connector cap. The TCM monitors engine load and clutch slip and varies the solenoid duty cycle accordingly. The solenoids have a 12 V operating voltage and a pressure range of 4.7 - 0 bar (68 - 0 lbf.in ).

The resistance of the solenoid coil winding for all PCV solenoids is 5.05 Ohms at 20 ºC (68 ºF).

Solenoid Valves

Three solenoid valves are located in the valve block. The solenoid valves are controlled by the TCM and converts electrical signals into hydraulic control signals to control dog clutch application.

The solenoid valve is an open/closed, on/off solenoid which is controlled by the TCM switching the solenoid to earth. The TCM also supplies power to the solenoid. The TCM energises the solenoid in a programmed sequence for clutch application for gear ratio changes and shift control.

The resistance of the solenoid coil winding for solenoid is between 10 to 11 Ohms at 20 ºC (68 ºF).

Park Lock Actuator - Magnetic Valve Control Solenoid

1. Solenoid in locked (energized) condition - park lock released
2. Solenoid in unlocked (de-energized) condition - park lock engaged
3. Park lock spool valve
4. Control solenoid
5. Claw locked
6. Claw unlocked

A control solenoid is located in the valve block. The solenoid is controlled by the TCM and converts electrical signals into hydraulic control signals to control the electronic park lock function.

The control solenoid is an on/off solenoid which is controlled by the TCM by switching the solenoid to earth.

When the Park lock is to be released, the park lock solenoid valve sends ATF pressure to the spool valve and moves it into contact with the claws of the solenoid. Movement of the spool valve moves the park rod and releases the park pawl from the park interlock gear. The control solenoid is energised by the TCM and the claws close to retain the spool valve in the unlocked position. A shuttle valve retains ATF pressure on the spool to prevent inadvertent park lock operation in the event of an electrical failure until the engine is stopped.

When the Park lock is to be engaged, ATF pressure is released from the spool valve and the TCM de-energises the control solenoid. The claws are released, the spool valve returns under spring pressure to the park lock position and the park lock is engaged. A Service Park Release (SPR) procedure must be performed to release the parking lock manually if an electrical failure occurs or the engine is not running.

To allow the vehicle to roll through a car wash, the control solenoid remains energised if the engine is stopped with the TCS in neutral. This holds the transmission out of park without hydraulic pressure for 10 minutes. After this time the control solenoid is de-energised, releasing the claws and allowing the spool valve to return to the park position.

The resistance of the solenoid coil winding is 25 Ohms at 20 ºC (68 ºF).

Solenoid Valves

Three solenoid valves are located in the valve block. The solenoid valves are controlled by the TCM and converts electrical signals into hydraulic control signals to control dog clutch application.

The solenoid valve is an open/closed, on/off solenoid which is controlled by the TCM switching the solenoid to earth. The TCM also supplies power to the solenoid. The TCM energises the solenoid in a programmed sequence for clutch application for gear ratio changes and shift control.

The resistance of the solenoid coil winding for solenoid is between 10 to 11 Ohms at 20 ºC (68 ºF).

Park Lock Actuator - Magnetic Valve Control Solenoid

1. Solenoid in locked (energized) condition - park lock released
2. Solenoid in unlocked (de-energized) condition - park lock engaged

1. Park lock spool valve
2. Control solenoid
3. Claw locked
4. Claw unlocked

A control solenoid is located in the valve block. The solenoid is controlled by the TCM and converts electrical signals into hydraulic control signals to control the electronic park lock function.

The control solenoid is an on/off solenoid which is controlled by the TCM by switching the solenoid to earth.

When the Park lock is to be released, the park lock solenoid valve sends ATF pressure to the spool valve and moves it into contact with the claws of the solenoid. Movement of the spool valve moves the park rod and releases the park pawl from the park interlock gear. The control solenoid is energised by the TCM and the claws close to retain the spool valve in the unlocked position. A shuttle valve retains ATF pressure on the spool to prevent inadvertent park lock operation in the event of an electrical failure until the engine is stopped.

When the Park lock is to be engaged, ATF pressure is released from the spool valve and the TCM de-energises the control solenoid. The claws are released, the spool valve returns under spring pressure to the park lock position and the park lock is engaged. A Service Park Release (SPR) procedure must be performed to release the parking lock manually if an electrical failure occurs or the engine is not running.

To allow the vehicle to roll through a car wash, the control solenoid remains energised if the engine is stopped with the TCS in neutral. This holds the transmission out of park without hydraulic pressure for 10 minutes. After this time the control solenoid is de-energised, releasing the claws and allowing the spool valve to return to the park position.

The resistance of the solenoid coil winding is 25 Ohms at 20 ºC (68 ºF).

Sensor Unit

1. 'PARK' (P) sensor
2. Pressure sensor connector
3. Speed sensor (torque converter turbine and output shaft)
4. Automatic Transmission Fluid (ATF) temperature sensor
5. Connector pins for pressure control valves, solenoid valves and park lock control solenoid
6. Connector board
7. Transmission electrical connector

The sensor unit is mounted on the valve block and secured with three screws. The sensor unit comprises a 26 pin electrical connector, a 'PARK' sensor, a pressure sensor connector, two speed sensors, ten solenoid connectors and an ATF temperature sensor.

The electrical connector is fitted with seals through a hole in the transmission main casing and secured with a spring clip.

The 'PARK' (P) sensor is located inside the main casing, adjacent to the electrical connector. The sensor is secured to a boss in the main casing with a screw. The 'PARK' sensor comprises a sliding switch which is operated by the selector shaft when it is moved by the park lock actuator.

Two speed sensors are used in the transmission and are located within the transmission housing and are connected to the sensor unit. The sensors take their speed reading from the slots in the clutch basket of the multiplate clutch E and the gear teeth of the spur pinion. The sensors provide input and output speed signals to the TCM. Both speed signals are received by the TCM which uses the signals to calculate engine torque output, shift timing and torque converter lock-up.

The fluid temperature sensor is integrated into the internal wiring harness within the transmission sensor unit. It detects the ATF temperature in the transmission and transmits a signal corresponding to the temperature to the TCM. The TCM monitors the temperature and adjusts clutch and brake application to provide smooth gear shifts across a wide range of temperatures and ATF viscosities.

Each solenoid is connected by two pins integral with the connector board.

Each solenoid pins is connected via a harness to the electrical connector.

Automatic transmission fluid (ATF) Pump

1. ATF filter
2. Intermediate plate
3. Drive pinion
4. Stator shaft
5. Drive chain
6. ATF pump

The ATF pump is located in an intermediate plate within the transmission main casing. The intermediate plate is attached to the inside of the transmission main casing with studs and nuts, behind the torque converter.

The intermediate plate contains the splined stator shaft, to which the torque converter stator is connected. The torque converter shell extends into and drives a drive pinion with an integral sprocket, which operates a roller drive chain to drive the ATF pump. The drive pinion is therefore rotated at engine speed.

The pump is located at the bottom of the transmission main casing and is attached to the housing with screws. An ATF filter ensures that any particulate matter is collected by the filter before the ATF enters the ATF pump.

The ATF pump is a vane cell pump which can produce a pressure of between 3.5 and 44.0 bar (50 and 638 lbf/in²) and a flow of 14.7 cm³ (0.9 in³). The pump can operate at speeds from 700 to 7800 Revolutions Per Minute (RPM) with a maximum speed of 8600 RPM.

Automatic Transmission  Transaxle / Component DescriptionDrive Clutches

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