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Electronic Automatic Transmission(EAT)-ZF




ELECTRONIC AUTOMATIC TRANSMISSION (EAT) - ZF

DESCRIPTION

General
The ZF 5HP24 transmission is an electronically controlled, five speed unit and is mated with the V8 Petrol engine. The transmission is controlled by an Electronic Automatic Transmission (EAT) ECU, which contains software to provide operation as a semi-automatic 'Steptronic' transmission. This allows the transmission to be operated as a conventional automatic unit by selecting P, R, N, or D on the selector lever. Movement of the selector lever across the gate to the 'M/S' position puts the transmission into electronic 'Sport' mode. Movement of the selector lever in a lateral position to the + or - positions puts the transmission into electronic manual 'Steptronic' mode.

OPERATION

Power Distribution
Feed from the positive battery terminal (C0192) is supplied to fusible link 2 and fuse 53 of the passenger compartment fuse box (C0632) on an R wire. A permanent battery feed is also supplied to the 50A fuse contained within the fuse holder (C1875) on an R wire. This fuse (C1876) provides a constant battery feed to the transfer box ECU (C3855) on a pair of R wires.

Fusible link 2 of the passenger compartment fuse box (C0591) provides a constant battery feed to the ECM relay (C1895) and fuse 4 of the engine compartment fuse box (C0570) on a pair of R wires. Operation of the ECM relay (C1895) is controlled by the ECM (C0604) on an N wire. The energised ECM relay (C3895) provides a feed to fuse 1 of the engine compartment fuse box (C0570) on an RW wire. Fuse 1 (C0570) is connected to the EAT ECU (C0932) by a pair of RU wires. The EAT ECU (C0932) is earthed on N wires.

Fuse 4 of the engine compartment fuse box (C0570) is connected to the EAT ECU (C0932) by an R wire.

Fuse 53 of the passenger compartment fuse box (C0583) is connected to the ignition switch (C0099) by an R wire. When the ignition switch is turned to the 'auxiliary' position, current flows across the switch (C0099) to fuse 37 of the passenger compartment fuse box (C0587) on a PB wire. Fuse 37 (C0587) provides an auxiliary ignition feed to the transfer box ECU (C3319) on a PU wire.

When the ignition switch is turned to the 'ignition' position, current flows across the switch (C0099) to fuse 5, fuse 33, and fuse 35 of the passenger compartment fuse box (C0585) on a G wire. Fuse 5 (C0587) provides an ignition feed to the EAT ECU (C3835) on a GW wire. Fuse 33 (C0587) provides an ignition feed to the transfer box ECU (C1319) on a GP wire. Fuse 35 (C0587) provides an ignition feed to the Hill Descent Control (HDC) switch (C0365) on a GBY wire.

EAT ECU
The EAT ECU controls operation of the transmission via the following:

Electronic Pressure Regulator Solenoids (EPRS)
The five EPRS located in the automatic transmission (C0244) are provided a Pulse Width Modulated (PWM) by the EAT ECU (C1835) on a P wire. The EAT ECU controls operation of the EPRS by providing earth paths on TB, R, B, K and YR wires.


NOTE: Wire colour TB IS transparent with a black tracer.


Shift Control Solenoids
The three shift control solenoids located in the automatic transmission (C0244) are provided a feed by the EAT ECU (C1835) on a YU wire. The EAT ECU (C3835) energizes the solenoids by providing earth paths on 0, G, and Y wires.

Turbine Speed Sensor
The turbine speed sensor acts as an input speed sensor. The EAT ECU (Cl835) provides a feed to the turbine speed sensor (C0244) on a U wire. The turbine speed sensor (C0244) returns an ac voltage pulse back to the EAT ECU (C1835) on an S wire. By measuring the peak to peak voltage of the voltage wave form, the EAT ECU can determine the speed of the turbine.

Output Shaft Speed Sensor
The EAT ECU (C1835) provides a feed to the output shaft speed sensor (C0244) on a W wire. The output shaft speed sensor (C0244) returns an ac voltage pulse back to the EAT ECU (C1835) on an N wire. By measuring the peak to peak voltage of the voltage waveform, the EAT ECU can determine the speed of the output shaft.

Transmission Temperature Sensor
The temperature of Automatic Transmission Fluid (ATF) is measured by the Negative Temperature Coefficient (NTC) transmission temperature sensor. The EAT ECU (C1835) provides a feed to the temperature sensor (C0244) on a BR wire. By measuring the voltage returned on a WR wire, the EAT ECU can determine ATF temperature.

Shift Interlock Solenoid
To lock the selector lever assembly, the EAT ECU (C0193) provides a feed to the shift interlock solenoid (C0673) on a BP wire. An earth path is provided by the EAT ECU (C0193) on an NP wire.

Steptronic
When manual (Steptronic) mode is selected, the EAT ECU selects gears according to inputs received from the Steptronic switch. The EAT ECU (C0193) provides two feeds to the Steptronic switch (C1664); one on a UY wire, one on a US wire. If a downshift is requested via the selector lever, a momentary earth is created. Current on the UY wire is allowed to flow across the switch to earth on an NB wire. Sensing this, the EAT ECU downshifts 1 gear.

If an upshift is requested via the selector lever, a momentary earth is created. Current on the US wire is now allowed to flow across the switch to earth on an NB wire. Sensing this, the EAT ECU upshifts 1 gear.
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