776D and 777D Off-Highway Truck/Tractors Hydraulic System Caterpillar

Illustration 1	g00634462
AGC1-1063 AGY1-80 Hoist control valve (1) Hoist proportioning solenoid for SNUB, FLOAT, and LOWER (2) Hoist proportioning solenoid for RAISE

Illustration 2	g01016881
AGC1064-UP AGY81-UP Hoist control valve (1) Hoist proportioning solenoid for SNUB, FLOAT, and LOWER (2) Hoist proportioning solenoid for RAISE

1. Use Caterpillar Electronic Technician (ET) in order to determine if there are any active diagnostics in the Power Train ECM for any of the following parameters:
   • Hoist raise solenoid current

   • Hoist lower solenoid current

   • Hoist lever position sensor

   If diagnostics are found, refer to Troubleshooting Section, "Power Train Electronic Control System" for the 69D, 769D, 771D, 773D, 773E, 775D, 775E, 776D, and 777D Off-Highway Trucks. If diagnostics are not found, proceed to step 2.

2. Install multimeters.

   1. Install a multimeter in series with hoist proportioning solenoid (1) .

   2. Install a multimeter in series with hoist proportioning solenoid (2) .

3. Monitor status parameters with the use of ET.

   1. Use Caterpillar Electronic Technician (ET) in order to monitor the following two status parameters in the transmission Electronic Control Module (ECM):
      • Hoist raise solenoid current

      • Hoist lower solenoid current

      Note: The Caterpillar Monitoring System can also be used to monitor the hoist raise solenoid current and the hoist lower solenoid current.

4. Take readings for the HOLD position.

   1. Move the hoist control lever to the HOLD position and start the engine.

   2. Record the readings for both status parameters that are displayed in ET.

   3. Record the readings that are displayed on both multimeters.

5. Take readings for the RAISE position.

   1. Move the hoist control lever to the RAISE position.

   2. Record the readings for both status parameters that are displayed in ET.

   3. Record the readings that are displayed on both multimeters.

   4. In preparation for the next step, raise the dump body to the dump position.

6. Take readings for the LOWER position.

   1. Move the hoist control lever to the LOWER position.

   2. Record the readings for both status parameters that are displayed in ET.

   3. Record the readings that are displayed on both multimeters.

7. Take readings for the FLOAT position.

   1. As the dump body is lowering, release the hoist control lever.

   2. Record the readings for both status parameters that are displayed in ET.

   3. Record the readings that are displayed on both multimeters.

8. Take readings for the SNUB position.

   1. Allow the dump body to contact the frame.

   2. Record the readings for both status parameters that are displayed in ET.

   3. Record the readings that are displayed on both multimeters.

9. Disconnect the tools that were used in the above procedure.

   1. Disconnect both multimeters.

   2. Disconnect Caterpillar Electronic Technician (ET)

10. Evaluate the readings that were taken in the above steps. Compare the recorded values with the values in Table 2.

    1. Calculate target values for table 2. Identify the formulas that are shown in the footnotes of table 2. Use these formulas and the appropriate readings from ET to obtain the calculated target values for table 2.

    2. For each position of the hoist control lever, compare the recorded readings from the multimeters to the values for table 2.

Problem: The values do not match the table.

Probable Cause

• The hoist control position sensor is not sending the correct signal to the Power Train Electronic Control Module (Power Train ECM). Use Caterpillar Electronic Technician (ET) to view the input signal to the Power Train ECM.

• The hoist proportioning solenoid or the wiring from the Power Train ECM has failed.

Note: The Caterpillar Monitoring System can also be used to view the input signal to the Power train ECM.