Description - 2
Electronic Automatic Transmission (EAT)
DESCRIPTION
Fluid Temperature Sensor
The fluid temperature sensor is located within the gearbox on the valve block. The EAT ECU uses this sensor to monitor the gearbox fluid temperature.
When the fluid is cold, the EAT ECU changes gear at higher engine speeds to promote faster fluid warm-up. If the fluid temperature becomes too high, the EAT ECU transmits a cooling request on the CAN link to the ECM to operate the cooling fans.
The fluid temperature sensor has an electrical output to pin 39 of the EAT ECU which also provides an earth path for the sensor.
The fluid temperature sensor is a negative temperature coefficient sensor. As the temperature rises, the resistance in the sensor decreases. As temperature decreases, the resistance in the sensor increases and the output voltage to the EAT ECU changes in proportion.
The output voltage from the sensor is in the range of 0 - 2.5 Volts with the lower voltage representing the highest temperature.
The change in resistance is proportional to the temperature of the gearbox fluid. From the resistance of the sensor, the EAT ECU calculates the temperature of the gearbox fluid. Should the fluid temperature sensor fail the EAT ECU uses the last recorded EAT ECU value as a default value.
Fluid Temperature Sensor Resistance Values
The fluid temperature sensor can fail in the following ways:
^ Sensor open circuit
^ Short circuit to 12 or 5 volts
^ Short circuit to earth.
The EAT ECU will detect temperature sensor failure when the vehicle speed exceeds 12.5 mph (20 km/h) and the temperature sensor provides a reading of less than -30°C (-22°F). In the event of a fluid temperature sensor signal failure any of the following symptoms may be observed:
^ Upshift to 5th gear inoperative
^ Torque reduction request from the EAT ECU to the ECM inoperative.
Selector and Inhibitor Switch
The selector and inhibitor switch is located on the selector shaft on top of the gearbox and connected to the main harness by a 10 pin connector (C0244).
While the ignition is on, the selector and inhibitor switch receives a battery voltage power feed from the main relay. In some markets, in order to illuminate the LED module whenever the key is in the ignition switch, the selector and inhibitor switch also receives a battery voltage power feed from an illumination relay installed behind the center console.
Where fitted, operation of the illumination relay is controlled by the passive coil on the ignition switch. When the key is installed in the ignition switch the illumination relay energizes to connect the power feed to the selector and inhibitor switch. When the main relay is energized by the ECM, the illumination relay de-energizes and the power feed to the selector and inhibitor switch is taken from the main relay.
The EAT ECU and the LED module are provided with a voltage output from the selector and inhibitor switch that corresponds with the gear position the driver has selected. Seven sets of contacts in the selector and inhibitor switch which are operated by the selector shaft. Each set of contacts corresponds to one of the seven selector lever positions (PRND421). Only one set of contacts will supply battery voltage to the EAT ECU and the LED module at any one time. The EAT ECU monitors the switch outputs every 10 ms.
A pair of contacts are provided for the crank inhibit circuit. The contacts are only closed when the selector lever is in the 'P' end 'N' positions.
The two contacts are wired in series with the EWS3D immobilization ECU. When the selector lever is in any position other than 'P' or 'N', the feed from the ignition switch to the immobilization ECU is broken by the open contacts, preventing starter motor operation.
In the event of a selector and inhibitor switch signal failure, any of the following symptoms may be observed:
^ Upshift to 5th gear inoperative
^ Torque converter lock-up inoperative
^ Torque reduction request from the EAT ECU to the ECM inoperative
^ Cranking disabled if fault is on the two inhibitor switch contacts.
Gear Selector Lever Assembly
The gear selector lever assembly comprises a shift lock solenoid, a key interlock mechanism (if fitted), an LED module and a sport/manual switch.
A nylon cast plate provides the location for the selector lever components. The plate is secured to the floor pan with six integral studs and nuts. A rubber boot protects the assembly from dirt and moisture under the vehicle and also isolates vibrations from the lever.
The selector lever is attached to a gimbal mounting which allows gear selection of PRND421 in a forward and backward direction and selection between automatic and sport/manual in a left and right transverse direction. When sport/manual mode is selected, the lever can be moved in a forward or backward direction to select + or - for manual operation.
There are seven selector lever positions:
^ P (Park) - prevents the vehicle from moving by locking the gearbox.
^ R (Reverse) - select only when vehicle is stationary and the engine is at idle.
^ N (Neutral) - no torque transmitted to the drive wheels.
^ D (Drive) - this position uses all five forward gears. Normal position selected for conventional driving.
^ 4 - this position uses 1st to 4th gears only.
^ 2 - this position uses 1st and 2nd gears only.
^ 1 - this position uses 1st gear only.
^ S/M (Sport/Manual - Steptronic) - this position uses all five gears as in 'D', but will shin up at higher engine speeds, improving acceleration.
^ + and - - movement of the selector lever in the +/- positions, when the selector lever is in the 'S/M' position, will operate the gearbox in manual (Steptronic) mode, allowing the driver to manually select all five forward gears.
The selector lever position is displayed to the driver on the LED module in the center console and in the instrument pack and corresponds with the position of the selector lever. The LED module illumination and instrument pack display is determined by the selector and inhibitor switch assembly on the gearbox, with the exception of the 'S/M' LED and the 'Sport' instrument pack display which are operated by a hall effect sensor located on the sport manual switch.
All vehicles with an automatic gearbox incorporate an interlock solenoid at the bottom of the lever, which, when the ignition switch is in position 11, prevents the lever being moved from Park unless the foot brake is applied.
Sport/Manual Switch
The sport/manual switch comprises a PCB and connector socket which is located to the left of the selector lever and is an integral part of the selector lever assembly and cannot be serviced separately. The switch is connected to the main harness by a twelve pin connector.
The sport/manual switch has five proximity sensors which correspond to the D, N, 4 and +/- positions. The selector lever has two targets. An upper target is aligned with the DN4 sensors and the lower target is aligned with the +/ sensors.
When the selector lever is in the D position, the D sensor is aligned with the target and the EAT ECU receives a signal that D is selected. When the selector lever is moved to the S/M (sport) position, the target moves away from the sensor. This is sensed by the ECU which then initiates sport mode.
The sensors in the N and 4 positions inform the ECU that D has been deselected, but not to the S/M position, preventing the ECU from incorrectly initiating sport mode.
When the selector lever is moved to the S/M position, the target moves away from the D sensor. If the EAT ECU does not receive a signal from either the 4 or N sensors, it determines that sport has been selected. The lower target is positioned between the two sensors for +/- selection. If the selector lever is not moved to the +/- positions, the ECU keeps the gearbox in sport mode. If the ECU senses a signal from either the + or - sensor, it initiates manual mode and selects the manual gear selection requested. Manual mode will be maintained until the ECU senses a signal from the D sensor.
Shift Interlock Solenoid
The shift interlock solenoid is controlled by the EAT ECU. When the ignition switch is in position 11, with the selector lever in the Park position, the EAT ECU supplies a power feed to the shift interlock solenoid. The shift interlock solenoid energizes and extends a pin into the selector lever, locking the lever in Park.
While the selector lever is in Park, when the EAT ECU senses the brake pedal being pressed, it de-energizes the shift interlock solenoid and the solenoid pin retracts, allowing the selector lever to be moved. When the selector lever is in any position other than Park, the shift interlock solenoid remains de-energized after the brake pedal is released, and the lever is free to be moved through the remainder of the range.
LED Module
The LED module is located in the selector lever surround and is secured with two integral clips. The module is connected to the main harness by a 12 pin connector (C0675).
The LED module illuminates the applicable LED for the P, R, N, D, 4, 2, 1 and S/M positions. When the side lamps are switched on, all the LED's are illuminated at a low intensity, with the selected gear lever position LED illuminated at a higher intensity.
Selector Cable
The selector cable is a Bowden type cable that connects the selector lever to an input lever on the gearbox.
A 'C' clip secures the outer cable to the selector lever assembly; the gearbox end of the outer cable is secured to a bracket on the gearbox by an integral clip. The inner cable is adjustable at the connection with the gearbox input lever
Brake Switch
The brake switch is located on the pedal box below the fascia. The EAT ECU uses this switch to monitor brake pedal application status. The information is input to pin 43 of the EAT ECU on a hardwired connection from the switch.
The EAT ECU can allow the gearbox to apply more engine braking therefore slowing down the vehicle in a shorter distance and reducing brake pad wear. The EAT ECU achieves engine braking by applying the low and reverse clutches.
The brake switch can fail in the following ways:
^ Switch open circuit
^ Short circuit to 12 or 5 volts
^ Short circuit to earth.
In the event of a brake switch signal failure, extra gearbox braking will not occur and the shift lock solenoid (if fitted) will not function.
Instrument Pack
The instrument pack displays gearbox selection and fault information in the LCD and can illuminate the MIL for OBD emission related faults.
The gearbox related displays in the instrument pack are controlled by the ECM which transmits CAN message signals to operate the lamps and the LCD.
Malfunction Indicator Lamp (MIL)
The MIL is an amber warning lamp located in the instrument pack. On all except WAS models, the warning lamp shows an engine silhouette. On NAS models the warning lamp shows a SERVICE ENGINE SOON legend. The lamp is illuminated by a CAN message from the ECM on receipt of a CAN message from the EAT ECU.
Emission related faults are detected by the OBD feature in the EAT ECU and will illuminate the MIL in the instrument pack.
Liquid Crystal Display (LCD)
The LCD is located in a central position in the instrument pack. In addition to displaying the odometer and trip meter, the LCD also displays the current gearbox status. The following table shows the characters displayed and their definition.
The EAT ECU transmits the selector lever position through the CAN bus to the ECM. The ECM processes this information and passes it to the instrument pack in the form of CAN messages to display the gearbox status.
If the gearbox develops a fault and adopts the limp home mode, the LCD will alternately display 'F' and 4" to alert the driver that a fault has occurred and limp home mode is operational.
Electronic Automatic Transmission (EAT) ECU
The EAT ECU is located in the Environmental box (E-box) in the engine compartment, adjacent to the ECM. The ECU is connected to the vehicle wiring by a 54 pin connector (C0932).
The EAT ECU uses a 'flash' Electronic Erasable Programmable Read Only Memory (EEPROM). This enables a new or replacement EAT ECU to be externally configured. EEPROM also allows the EAT ECU to be updated with new information and market specific data.
The EAT ECU memorizes the signal values of the gearbox sensors and actuators. These stored values ensure optimum gearbox performance is achieved at all times.
This information is lost if battery voltage is too low, for example if the battery becomes discharged. The EAT ECU reverts to default readings on first engine start after a battery discharge or disconnection. The EEPROM facility in the ECU allows the stored values to be re-learned, ensuring optimum gearbox performance.
If these signals are not within the EAT ECU stored parameters, the ECU will make adjustments to the operation of the gearbox through the actuators to provide optimum driveability and performance.
The inputs from the sensors constantly updates the EAT ECU with the current operating condition of both the gearbox and the engine. The ECU compares this current information with mapped information stored within its memory. The ECU will make any required adjustment to the operation of the gearbox through the following actuators:
^ Gear control solenoid valves
^ Lock-up solenoid valve
^ Line pressure solenoid valve.
The EAT ECU also interfaces with the following:
^ Engine Control Module (ECM) via the CAN
^ Instrument pack via the CAN
^ Diagnostic socket via the ISO 9141 K line.
Connector C0932 Pin Details
The table shows the harness connector face view and pin numbers and input/output information.
Main Relay
The main relay is located in the engine compartment fusebox and supplies battery voltage to the EAT ECU, in addition to other vehicle components. The main relay is energized by the ECM when the ignition is switched on.
When the ignition is switched off, the ECM will maintain the main relay in an energized state for several minutes. This allows for cooling fan operation to continue after the engine has been switched off and allows other vehicle ECU's to remain active. The EAT ECU remains active for a short period after the ignition is switched off to allow EEPROM fault code data to be stored.
In the event of a main relay failure, any of the following symptoms may be observed:
^ The gearbox will be locked in 4th gear (limp home mode)
^ No CAN communications will be available.