Description and Operation - Diagnostics

Diagnostics





A diagnostic socket allows the exchange of information between the EAT ECU and TestBook/T4. The diagnostic socket is located behind the center console, in the passenger footwell. The diagnostic socket is connected to the EAT ECU on an ISO 9141 K Line. The system uses a 'P' code diagnostic strategy and can record faults relating to gearbox operation. The codes can be retrieved using TestBook/T4 or any diagnostic tool using Keyword 2000 protocol.

Diagnostic Trouble Codes (DTC)
The following table lists P codes, affected components and fault description.








The diagnostics related to diagnostic trouble codes introduced by ECD3 are disabled on vehicles built prior to the ECD3 compliance date.
Controller Area Network (CAN) Bus
The CAN bus is a high speed broadcast network between the ECM, instrument pack, ABS ECU and the EAT ECU allowing fast exchange of data between the ECU's every few microseconds.

The bus comprises two wires which are identified as CAN low (L) and CAN high (H). The wires are twisted together to minimize the electromagnetic interference (noise) produced by the CAN messages.

To prevent message errors from electrical reflections, 120 Ohm resistors are incorporated into the CAN wire terminals of the ECM, instrument pack, ABS ECU and the EAT ECU.

CAN messages consist of a signal which is simultaneously transmitted, in opposite phase, on both wires. CAN L switches between 2.5 and 1.5 volts, while CAN H switches between 2.5 and 3.5 volts. This causes a potential difference between the two lines to switch between 0 volt (logic 1) and 2 volts (logic 0) to produce the digital signal message.

In the event of a CAN bus failure any of the following symptoms may be observed:
^ Transmission defaults to 4th gear
^ Torque converter lock-up control is disabled
^ Transmission of torque reduction message to the ECM is inhibited.





CAN Bus Switching

EAT ECU CAN Messages





The table lists CAN message inputs and outputs from and to the EAT ECU.

CAN Inputs
^ Actual engine torque. This message from the ECM indicates the actual engine torque produced at any one time. The EAT ECU uses this message to control gear shift scheduling.
^ Engine coolant temperature. This message from the ECM is used by the EAT ECU for OBD diagnostic functions and to detect when the engine has completed a 'warm up' cycle.
^ Engine friction. This message from the ECM is the current frictional torque losses within the engine and is expressed as a percentage of maximum engine torque. The EAT ECU uses this message to control gear shift scheduling.
^ Engine speed. This message from the ECM is used by the EAT ECU to calculate gearbox oil pressure to assist control of gear shift scheduling.
^ Engine speed signal error. This message from the ECM informs the EAT ECU if there is a fault with the engine speed calculation. If necessary, the EAT ECU then adjusts gearbox operation to prevent possibility of mechanical damage.
^ Engine torque error. This message from the ECM informs the EAT ECU that torque values received are incorrect and there is an ECM torque measurement error.
^ Estimated engine torque. This message from the ECM informs the EAT ECU of the level of torque that the engine is producing. The EAT ECU uses this message to control gearshift scheduling.
^ Ignition switch status. This message from the ECM is produced when the ECM energizes the main relay. The EAT ECU uses this message to initiate the power-down routine at ignition off.
^ Actual engine torque. This message from the ECM is the theoretical engine torque for current throttle setting and engine operating conditions. This is the same as the actual engine torque unless torque reduction in progress and is expressed as a percentage of maximum engine torque. The EAT ECU uses this message to control gear shift scheduling.
^ Throttle angle. This message from the ECM informs the EAT ECU of the throttle angle (driver demand). The EAT ECU uses this message to control gear shift scheduling.
^ Torque reduction status. This message from the ECM informs the EAT ECU of the success of a torque reduction request.
^ Engine MIL status. This message from the ECM indicates to the EAT ECU that the MIL has been illuminated by the ECM. The EAT ECU will disable OBD fault monitoring.
^ Hill descent activity status. This message from the ABS ECU informs the EAT ECU that HDC has been requested. Providing the selector lever is in position 1 or R. the EAT ECU enters HDC mode and assists the ABS with engine braking.

CAN Outputs
^ Cooling request. Request for additional cooling of the transmission fluid. The ECM switches on, or increases the speed of the cooling and, if fitted, condenser fans.
^ Current/Target gear. Informs the ECM what gear is currently engaged or, if a gear shift is in progress, the gear to which the gearbox is shifting. Used by the ECM for engine load change prediction.
^ Gear selector lever position. The EAT ECU transmits a signal to the ECM of the gear selector lever position selected by the driver. The ECM outputs a CAN message to the instrument pack to display the selection in the LCD
^ Gear shift in progress. Informs the ECM when a gear shift is in progress. Used at idle speed to compensate for engine load changes during the gear shift.
^ Gearbox fault status. The EAT ECU uses this signal to display the status of the EAT ECU. If a gearbox fault occurs, the EAT ECU will generate this message to alternately display 'F' end '4' in the instrument pack LCD and initiate the default strategy for the gearbox.
^ Torque reduction request. Requests the ECM to reduce engine torque for a gear shift (equivalent to lifting off the throttle in manual gearbox models). Amount of torque reduction required expressed as a percentage of maximum engine torque.
^ Gearbox MIL status. The EAT ECU transmits a signal to the ECM that there is a gearbox fault which will increase emissions above an acceptable level. The ECM outputs a message to the instrument pack which illuminates the MIL.
^ Gear shift mode. This signal is used to display the currently selected gearshift mode, drive, sport or manual, in the instrument pack LCD. This signal is originated from the EAT ECU.









JATCO Automatic Gearbox Control Diagram