794 AC Off-Highway Truck Electronic Control System Caterpillar

Replacement of the Electronic Control Module (ECM) can be costly. Replacement can also be a time consuming task. Most electronic failures occur in the wiring and connectors. Prior to replacing an ECM, contact the Technical Communicator at your dealership for a possible consultation with Caterpillar. This consultation may greatly reduce repair time and expense.

When troubleshooting has indicated that the ECM has failed, temporarily mount a new ECM to the side of the suspect ECM. Test the Machine with the new ECM. If the problem no longer exists, proceed with the following steps.

Replacement of the ECM

Illustration 1	g03406057
Typical "Copy Configuration" in Cat® ET help menu

1. Record and save configuration data plus any customer specified parameters from the failed ECM.

   Refer to the help screen in Caterpillar^® Electronic Technician (Cat^® ET), shown in Illustration 1. Follow the instructions listed under "Using Service" - "Using Copy Configuration" - "Using ECM Replacement". These instructions cover how to load and save the configuration data from the ECM to be replaced. When complete, the "Program ECM" button will be enabled. Later, the "Program ECM" button will be used to load the configuration data into the new ECM.

   Refer to Troubleshooting, "Electronic Service Tool Does Not Communicate" if Cat^® ET will not communicate.

   1. Obtain the customer passwords and record the customer passwords. Refer to Troubleshooting, "Customer Passwords" if the customer has lost the passwords.

   2. Use Cat^® ET to access read customer specified parameters from the ECM.

   3. Record customer parameters on the "Customer Specified Parameters Worksheet".

2. Replace the faulty ECM.

   1. Turn the key start switch and the disconnect switch to the "OFF" position.

   2. Disconnect the machine harness connectors J1 and J2 from the ECM that is to be replaced.

   3. Remove the ECM and ensure that the replacement ECM has the same part number as the ECM that is being replaced.

   4. Connect the machine harness to the new ECM and mount the ECM.

   5. Connect the machine harness connectors J1 and J2 to the new ECM. Ensure that the connectors are fully seated. Ensure that the hold down bolt is tightened securely

   6. Turn the key start switch and the disconnect switch to the "ON" position.

3. Determine whether the ECM has been programmed and if necessary, flash program the ECM

   1. Connect Cat^® ET to the service tool connector and establish communication with the ECM that has been replaced.

      Cat^® ET will provide access to the new ECM, if the ECM has already been programmed. If the ECM has not been programmed use the "WinFlash" software which is contained in Cat^® ET. Refer to the Testing and Adjusting, "Electronic Control Module (ECM) - Flash Program" in this manual.

4. Obtain the factory passwords.

   1. Record the machine hours from the hour meter.

   2. Use Cat^® ET to access the system configuration parameters. When the factory password screen appears, record the following information on the "factory passwords worksheet". ECM Serial Number, Engine Serial Number, Number Of the Service Tool and Total Tattletales

   3. Leave Cat^® ET on the factory password screen and obtain passwords by providing the information on the "factory passwords worksheet".

5. Load/program all system configuration data plus customer parameters.

   1. Load/program all system configuration data before exiting the factory password screen.

      Use the "Program ECM" button in Cat^® ET to load the configuration data into the new ECM. Refer to "Programming the ECM" shown in Illustration 1.

   2. With Cat^® ET, select the "Service" option from the drop-down menu. Then, select the "Configuration" option. A list of items will appear. Check each item in this list to verify that the setting matches the machine configuration.

   3. Enter the original values in the "Read/Change Customer Specified Parameters". Obtain these values from the worksheet.

      If the parameters are not entered, new passwords are required.

      Note: If the customer specified parameters are entered before the system configuration data, the total tattletales will change. A new set of factory passwords will be necessary to access the system configuration parameters.

6. Perform all applicable system calibrations.

   Calibrate the following:

   • Swashplate Angle Sensor - refer to Testing and Adjusting, UENR0445, "Swashplate - Calibrate"

   • Proportional Hydraulic Modulating Valves - refer to Testing and Adjusting, UENR0445, "Main Control Valve - Calibrate"

   • Joysticks, Thumbwheels, and Attachment Pedals - refer to Testing and Adjusting, UENR0445, "Joystick and Pedal - Calibrate"

   Note: Calibrate the swashplate angle sensor before performing the ACS valve calibration (Proportional Hydraulic Modulating Valves).

   Note: Machine performance may be affected by any calibration procedures that are not performed.