System Description

TRANSMISSION - ZF 4HP 22 E
The electronic transmission system fitted to normally aspirated 4.0 liter vehicles comprises the following components:
- ZF 4HP 24 E Automatic Transmission
- Rotary selector switch
- Electronic Transmission Control Module
- Decoder Module
- Performance Mode Switch
- Kickdown Switch
- Gear Selection Illumination Module

System control is effected by the transmission control module (TCM), located behind the passenger side fascia, which continuously monitors requests made by the driver via the gear selector, throttle pedal etc. This data is used in conjunction with the speed input from the transmission and inputs from the engine management system,to calculate optimum shift points and control parameters for shift pressure and ignition retardation to enhance shift quality and reduce transmission unit wear.

The TCM is also able to detect faults within the system and store the relevant fault codes for interrogation with diagnostic equipment.

Gear shifts are controlled by three solenoid valves, and a pressure control regulator, located on the valve block within the transmission unit assembly. If a serious fault occurs, the TCM removes all electrical power from these valves and the transmission system reverts to a mechanical default condition. This condition allows only mechanical selection of reverse and one forward gear, either third or fourth, depending on prevailing conditions at the time of the default.

The decoder module receives inputs from the rotary switch and decodes these to drive one of six possible outputs, illuminating the correct gear indicator on the gear selector illumination module.

The performance mode switch and kick-down switch are used to adjust transmission operation as required by the driver. Performance mode selection, made via a switch mounted on the gear selector mechanism surround, can be either NORMAL, for everyday use, or SPORT, for enhanced performance. Kick-down is activated by a switch mounted below the accelerator pedal and is used to initiate a downward gear change, increasing torque and acceleration.