Circuit Operation
Electronic Automatic Transmission (EAT)
OPERATION
General
Feed from the positive battery terminal (C0192) is supplied to the main relay and fusible link 3 (C0632) on an R wire. Both are located in the engine compartment fuse box.
The battery also provides a feed to fusible link 4 of the engine compartment fuse box (C0632) on vehicles fitted with an instrument dimmer switch. For more information, refer to the Interior Lamps.
Operation of the main relay (C0576 on Td4 vehicles, C0578 on KV6 vehicles) is controlled by the Engine Control Module (ECM) (C0603 on Td4 vehicles, C0604 on kV6 NAS vehicles, C0371 on kV6 ROW vehicles) on a WK wire (NG on KV6 NAS vehicles). The energized main relay allows a battery feed to flow to fuse 4 of the engine compartment fuse box. Fuse 4 (C0575) provides a feed to the following on NK wires:
- The Automatic Transmission Control Unit (ATCU) (C0932).
- The transmission selector (C0244) (vehicles without instrument dimmer only).
- The illumination relay (C1976) (vehicles with instrument dimmer only).
- The Steptronic switches (C0410).
For further details of main relay operation, refer to the Engine Management - EDC, Engine Management - Siemens (NAS) or Engine Management - Siemens (All Except NAS).
Fusible link 3 (C0571) is connected to the ignition switch (C0028) by an N wire. When the ignition switch is turned to the 'ignition' position, current flows across the switch (C0028) to fuse 35 of the passenger compartment fuse box (C0588) on a G wire. Fuse 35 (C0580) provides an ignition feed to the transmission inhibit switch (C0244) on a W wire.
ATCU
The ATCU monitors the operation of the automatic gearbox via four sensors:
- The temperature of the automatic transmission fluid (ATF) is measured by the fluid temperature sensor. The fluid temperature sensor (C0243) receives a feed from the ATCU (C0932) on a WK wire. The temperature sensor return (C0243) to the ATCU (C0932) is via a KB wire. As the temperature of the ATF rises, so the resistance of the sensor decreases. The ATCU registers this drop in resistance and calculates the temperature of the ATF accordingly. For more information on the fluid temperature sensor, refer to the Automatic Gearbox - Jatco.
- Vehicle speed is measured by the vehicle speed sensor. The vehicle speed sensor (C0243) is connected to the ATCU (C0932) by a U wire. The speed sensor creates a sinusoidal waveform, with each positive phase of the waveform representing one tooth on the parking gear (19 per engine revolution). The ATCU uses this waveform to calculate vehicle speed. The sensor return (C0243) to the ATCU (C0932) is via a W then KB wire. For more information on the vehicle speed sensor, refer to the Automatic Gearbox - Jatco.
- Input shaft speed into the gearbox is measured by the turbine sensor. The turbine sensor (C0243) is connected to the ATCU (C0932) by an R wire. The turbine sensor creates a sinusoidal waveform, with 16 positive phases representing one input shaft revolution. The ATCU uses this signal along with a vehicle speed signal to calculate if the correct gear has been selected. The sensor return (C0243) to the ATCU (C0932) is via a U then KB wire. For more information on the turbine sensor, refer to the Automatic Gearbox - Jatco.
- The internal, or intermediate, transmission speed is measured by the intermediate sensor. The intermediate sensor (C0243) is connected to the ATCU (C0932) by an R wire. The intermediate sensor creates a sinusoidal waveform, with each positive phase of the waveform representing one tooth of the output gear (49 per revolution). The ATCU uses this signal to ensure the correct gear is engaged, and to monitor the amount of slip within the gearbox. The sensor return (C0243) to the ATCU (C0932) is via a B then KB wire. For more information on the intermediate sensor, refer to the Automatic Gearbox - Jatco.
Park
When park is selected, a main relay feed is able to flow from the transmission selector/inhibit switch (C0244) to the ATCU (C0932) and the selector indicator (C0675) on a KO wire. The 'P' symbol on the selector housing will now illuminate.
NOTE: On Canadian specification vehicles, a feed is also provided to the Central Control Unit (CCU) (C0593) on a KO wire. This input is used by the CCU to extinguish the daylight running lamps.
Reverse
When reverse gear is selected, a main relay feed is able to flow from the transmission selector/inhibit switch (C0244) to the reverse lamp relay (C0935) on an NG wire. The reverse lamp relay (C0935) is earthed on a B wire and controls operation of the reverse lamps. For more information on reverse lamp operation, refer to the Brake and Reverse Lamps.
A main relay feed is also supplied to the ATCU (C0932) and the selector indicator (C0675) on NG wires. The 'R' symbol on the selector housing will now illuminate.
If the vehicle is travelling forwards at greater than 6 mph (10 kph), the ATCU (C0932) provides a feed to the Low Coast solenoid (C0243) on a K wire. The Low Coast solenoid (C0243) is earthed via the ATCU (C0932) on an SB wire. When the Low Coast solenoid receives this feed, it drains the transmission fluid from the reverse clutch, thus preventing reverse gear from being selected.
Neutral
When neutral is selected, a main relay feed is able to flow from the transmission selector/inhibit switch (C0244) to the ATCU (C0932) and the selector indicator (C0675) on a WU wire. The 'N' symbol on the selector housing will now illuminate.
Drive
When drive is selected, a main relay feed is able to flow from the transmission selector/inhibit switch (C0244) to the ATCU (C0932) and the selector indicator (C0675) on a WB wire. The 'D' symbol on the selector housing will now illuminate.
When drive is selected, the ATCU (C0932) receives signals from the vehicle speed sensor (C0243) housed within the gearbox on a U wire. The sensor (C0243) is earthed via ATCU (C0932) on a W then KB wire. The ATCU (C0932) also receives a throttle pedal signal from the ECM (C0331 on Td4 and KV6 NAS vehicles, C0371 on KV6 ROW vehicles) via the CAN- BUS on YN (Low) and YB (High) wires. The ATCU uses this information to select the appropriate gear by operating the gearbox shift solenoids as follows:
1st Gear
To select first gear, shift solenoid B and shift solenoid C are operated. The ATCU (C0932) will provide a feed to shift solenoid B (C0243) on an O wire. Shift solenoid C (C0243) receives a feed from the ATCU (C0932) on an OU wire.
2nd Gear
To select second gear, shift solenoid A and shift solenoid B are operated. The ATCU (C0932) will provide a feed to shift solenoid A (C0243) on an R wire. Shift solenoid B (C0243) receives a feed from the ATCU (C0932) on an O wire.
3rd Gear
To select third gear, only shift solenoid B is operated. The ATCU (C0932) will provide a feed to shift solenoid B (C0243) on an O wire.
4th Gear
To select fourth gear, only shift solenoid C is operated. The ATCU (C0932) will provide a feed to shift solenoid C (C0243) on an OU wire.
5th Gear
To select fifth gear, shift solenoid A and shift solenoid C are operated. The ATCU (C0932) will provide a feed to shift solenoid A (C0243) on an R wire. Shift solenoid C (C0243) receives a feed from the ATCU (C0932) on an OU wire.
4
When 4 is selected, a main relay feed is able to flow from the transmission selector/inhibit switch (C0244) to the ATCU (C0932) and the selector indicator (C0675) on an RG wire. The '4' symbol on the selector housing will now illuminate.
When 4 is selected, only the lowest 4 gears will be operable. For more information, refer to the Drive section.
2
When 2 is selected, a main relay feed is able to flow from the transmission selector/inhibit switch (C0244) to the ATCU (C0932) and the selector indicator (C0675) on an OB wire. The '2' symbol on the selector housing will now illuminate.
When 2 is selected, only the lowest 2 gears will be operable. For more information, refer to the Drive section.
1
When 1 is selected, a main relay feed is able to flow from the transmission selector/inhibit switch (C0244) to the ATCU (C0932) and the selector indicator (C0675) on a GY wire. The '1' symbol on the selector housing will now illuminate.
When 1 is selected, only first gear will be operable. For more information, refer to the Drive section.
Mode Selection
Sport Mode
The selector lever (C0410) is provided a main relay feed via fuse 4 of the engine compartment fuse box (C0575) on an NK wire. When the lever is moved across to the 'S/M' position, the selector lever (C041 0) provides a feed to the ATCU (C0932) on an LGK wire. The ATCU will now enter sport mode. In sport mode, the gearbox still operates as a conventional automatic transmission, but the unit becomes more responsive to driver demands. The selector lever (C0410) is earthed on a B wire.
The selector lever (C0410) also provides a feed to the selector indicator (C0675) on an LGK wire, illuminating the 'S/M' symbol on the selector housing.
Manual (Steptronic) Mode
When in sport mode, if the selector lever is moved to the '+' or positions, the gearbox will automatically enter manual (Steptronic) mode. When the selector lever is moved to the position, it provides a feed to the ATCU (C0932) on a GK wire. When the selector lever is moved to the '+' position, it provides a feed to the ATCU (C0932) on a GB wire. Manual gear changes can now be performed sequentially using the selector lever.
Cruise Control Mode - Td4
The cruise control master switch is located on the center console, below the radio. When cruise control is activated, the cruise control interface unit (C1959) provides a feed to the ATCU (C0932) on a WU wire. In cruise control mode, the ATCU uses a dedicated gearshift map to control the gearbox and assist the cruise control ECU in maintaining the vehicle speed at the required level.
For more information on cruise control operation, refer to the Cruise Control- KV6 (NORTH AMERICA).
Cruise Control Mode - KV6
The cruise control master switch is located on the center console, below the radio. When cruise control is activated, the cruise control ECU (C0239) provides a feed to the ATCU (C0932) on a WU wire. In cruise control mode, the ATCU uses a dedicated gearshift map to control the gearbox and assist the cruise control ECU in maintaining the vehicle speed at the required level.
For more information on cruise control operation, refer to the Cruise Control- KV6.
Hill Descent Control (HDC) Mode
In HDC mode, the ATCU applies engine braking to assist the ABS ECU in controlling the vehicles descent. HDC mode is activated if all of the following conditions exist:
- The gear selector lever is in position '1' or 'R'.
- The HDC switch is depressed.
- The throttle pedal is released.
The ATCU (C0932) communicates with the ABS ECU (C0501) via the CAN-BUS on YB (High) and YN (Low) wires. For more information on the CAN-BUS, refer to the Information Bus.
Fluid Pressure Control
Fluid pressure within the automatic gearbox is controlled by the Line Pressure solenoid. When required, the ATCU (C0932) provides a Pulse Width Modulated (PWM) signal to the Line Pressure solenoid (C0243) on a Y wire. The solenoid (C0243) is earthed via the ATCU (C0932) on an SB wire. For more details on fluid pressure control, refer to the Automatic Gearbox - Jatco.
Torque Converter Lock-Up
When the gearbox is in 4th or 5th gear, and the ATCU registers a high vehicle speed combined with a small throttle angle, the ATCU will lock the torque converter. This will enable maximum power to be transmitted to the road wheels. When this occurs, the ATCU (C0932) provides a PWM signal to the Lock-Up solenoid (C0243) on a U wire. The solenoid (C0243) is earthed via the ATCU (C0932) on an SB wire. For more details on torque converter lock-up, refer to the Automatic Gearbox - Jatco.
Shift Interlock
When the ignition switch is in the 'ignition' position and the selector lever is in the 'Park', the ATCU (C0932) provides a feed to the shift interlock solenoid (C0268) on a GW wire locking the selector lever in the 'Park' position. When the brake pedal is pressed, the brake pedal switch (C0652) provides a feed to the ATCU (C0932) on a GR wire. Sensing the brake pedal has been pressed the ATCU withdraws the feed to the shift interlock solenoid, releasing the selector lever.
The shift interlock solenoid (C0268) is earthed on a B wire.
Diagnostic Socket
If the ATCU detects a failure in an associated component, a fault code will be stored in its memory. Test Book or T4 can be used via the diagnostic socket to retrieve these fault codes to identify the cause of the failure. The diagnostic socket (C0040) is connected to the ATCU (C0932) by a K wire.