Discovery 2. Manual — part 143

AUTOMATIC GEARBOX - ZF4HP22 - 24

DESCRIPTION AND OPERATION

44-3

1 Transmission high/low switch
2 Mode switch
3 Gear position switch connector
4 Solenoid valve/speed sensor connector
5 Electronic automatic transmission ECU
6 Engine control module
7 Diagnostic socket
8 Instrument pack
9 Transmission fluid temperature sensor

10 Body control unit
11 Battery power supply
12 Ignition power supply

AUTOMATIC GEARBOX - ZF4HP22 - 24

44-4

DESCRIPTION AND OPERATION

Description

General
The automatic gearbox is a four speed unit with electronic control of gear selection, shift quality and torque converter
lock-up. Selections on the selector lever assembly are transmitted to the gearbox by a selector cable. A gear position
switch on the gearbox transmits the gear selection to an Electronic Automatic Transmission (EAT) ECU, which
outputs the appropriate control signals to an electro-hydraulic valve block in the gearbox. A mode switch enables the
driver to change the control mode of the EAT ECU. The EAT ECU operates warning lamps in the instrument pack to
indicate the control mode and system status.

The gearbox features a pressure lubrication system and is cooled by pumping the lubricant through an oil cooler.

On NAS market vehicles from 03 model year, the ZF 4HP24 transmission unit is introduced for use with the 4.6 litre
V8 engine. This transmission is required to accomodate the increased power output of the larger engine. The ZF
4HP22 transmission remains in use on vehicles with Td5 and 4.0 litre V8 engines.

Both transmission units are of similar construction, with the ZF 4HP24 unit being 15 mm longer than the 4HP22 unit
to accomodate a larger fluid pump. The operation of both transmission units is the same.

AUTOMATIC GEARBOX - ZF4HP22 - 24

DESCRIPTION AND OPERATION

44-5

Selector lever assembly

1 Release button
2 Mode switch
3 Electrical connector
4 Interlock solenoid (where fitted)
5 Base

6 Gasket
7 Securing bolt
8 Lever
9 Cover

10 Position indicators

The selector lever assembly consists of a lever and a cover attached to a base. The base is located on a gasket and
secured to the transmission tunnel. The lever is hinged to the base. A latch in the lever engages with detents in the
base to provide the lever positions P, R, N, D, 3, 2, 1. The latch is disengaged by pressing a release button on the
lever knob. Except for lever movement between positions D and 3, the button must be pressed before the lever can
be moved. In some markets, vehicles incorporate an interlock solenoid at the bottom of the lever, which prevents the
lever being moved from P unless the ignition switch is in position II and the foot brake is applied. If the battery
becomes flat, the interlock system will prevent selector lever movement and removal of the ignition key.

The cover incorporates lever position indicators and the mode switch. The lever position indicators illuminate to show
the position of the selector lever. Illumination is controlled by the Body Control Unit (BCU). The mode switch is a non-
latching hinged switch that, when pressed, connects an earth to the EAT ECU to request a change of mode.

An electrical connector at the rear of the cover connects the selector lever assembly to the vehicle wiring.

Selector cable
The selector cable is a Bowden type cable that connects the selector lever assembly to a selector lever on the
gearbox. 'C' clips secure the ends of the outer cable to brackets on the selector lever assembly and the selector lever.
The inner cable is adjustable at the connection of the inner cable with the gearbox selector lever.

AUTOMATIC GEARBOX - ZF4HP22 - 24

44-6

DESCRIPTION AND OPERATION

Gearbox

Diesel gearbox shown, V8 gearbox similar

1 Torque converter
2 Torque converter housing
3 Fluid pump
4 Breather tube
5 Intermediate plate
6 Gearbox housing
7 Rear extension housing
8 Electrical connector
9 Gear position switch

10 Selector lever
11 Mounting bracket

12 Heat shield
13 Rubber mounting
14 Gasket
15 Sump
16 'O' ring seal
17 Drain plug
18 'O' ring seal
19 Filler/level plug
20 Bolt
21 Clamp