Overview (G1772595): Overview

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The ZF 8HP70 transmission is an electronically controlled, hydraulically operated, 8 speed automatic unit. The hydraulic and electronic control elements of the transmission, including the TCM (Transmission Control Module), are incorporated in a single unit located inside the transmission and is known as Mechatronic valve block.

The ZF 8HP70 transmission has the following features:

Designed to be maintenance free
Automatic Transmission Fluid (ATF) is 'fill for life'
The torque converter features a controlled slip feature with electronically regulated control of lock-up, creating a smooth transition to the fully locked condition
Shift programs controlled by the TCM
ASIS (adaptive shift strategy), to provide continuous adaptation of shift changes to suit the driving style of the driver, which can vary from sporting to economical
Connected to the ECM (Engine Control Module) via the HS (High Speed) CAN (Controller Area Network) Powertrain bus for communications
Default mode if major faults occur
Diagnostics available from the TCM via the HS CAN Powertrain bus.

The higher fuel efficiency of the ZF 8HP70 automatic transmission is mainly due to the following modifications:

A wider ratio spread and more gears for better adaptation to ideal engine operating points
Significantly reduced drag torque in the shift elements (only two open shift elements per gear)
Use of a more efficient double stroke vane type ATF pump
Decoupling of the transmission when the vehicle is at standstill
Improved torsion damping in the converter.

The transmission selections are made using the rotary TCS (Transmission Control Switch) in the floor console.

Refer to: EXTERNAL CONTROLS (Description and Operation).

On vehicles featured with Start/Stop system, the 8HP70 Automatic Transmission is fitted with a HIS (Hydraulic Impulse Storage) device to ensure ATF is available to the shift elements as quickly as possible when the engine is started.