Automatic gearbox - ZF4HP22/24 (Description): 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.

Selector lever assembly