ZF-4HP24

The ZF-4HP24 transmission utilizes a microprocessor equipped transmission control unit (TCU) to control solenoid and pressure control valves. The TCU continuously monitors the gear selected, output shaft speed and throttle position. This information, and input from the engine control unit (ECU) is used to select the most suitable gear range for current driving conditions.

Transmission modes

An additional transmission mode for first gear delete has been added to the ZF-4HP24E transmission control. The mode switch is a three-way rocker type for selecting NORMAL, SPORT or DELETE FIRST modes. The instrument pack has indicators that illuminate when SPORT or DELETE FIRST modes are selected.

Delete first mode provides a second gear start-off to help prevent wheel spin on road surfaces with poor traction. If delete first is selected and the gear selector is in DRIVE, the transmission will momentarily engage first gear before engaging second gear.


Transmission ECU

The transmission ECU is revised to incorporate the delete first gear mode control. The ECU connects to the serial communications data link for JDS diagnosis.


Transmission fluid cooler connections

The radiator couplings for the transmission fluid cooler are push-on connections that require service tool ID 182 for removal.


Gear shift interlock


A gear shift interlock system is introduced for 1993 model year. The system prevents movement of the gear selector from PARK unless the ignition switch is in position II and the brake pedal is applied. In addition, the ignition key cannot be removed from the ignition switch unless the gear selector is in PARK. Once the key is removed, the selector is locked in PARK.