The Caterpillar Underspeed Control System varies the hydraulic pump flow in order to maintain the correct engine speed. The power shift pressure sensor is used to measure power shift pressure during the calibration procedure. After the calibration is complete, the ECM will use engine speed, throttle inputs, and calibration data in order to control the flow of the hydraulic pump. The output of the pump is controlled by adjusting the PWM signal to the power shift solenoid.
Power shift hydraulic pressure is at a maximum when the signal for the duty cycle to the power shift solenoid is at a maximum. The pressure will decrease as the duty cycle is decreased. ET has an override that is available to manually control the signal to the power shift solenoid.
Note: If the operation of the machine hydraulics system is unstable and there are no Active Diagnostic Codes, refer to Troubleshooting, "Unstable Hydraulic Function".
Note: The term "power shift" does not refer to the transmission of the machine.
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| Illustration 1 | g00671263 |
Schematic | |
Test Step 1. Check for Connector Damage.
- Turn the circuit breaker for the battery to the OFF position.
- Turn the keyswitch to the OFF/RESET position.
- Thoroughly inspect ECM connector J1/P1, ECM connector J2/P2, machine connector J3/P3, and power shift solenoid connector J113/P113. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
- Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).
- Check the customer connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).
- Check the harness and the wiring for abrasion and pinch points.
Expected Result:
All connectors, pins, and sockets should be completely inserted and coupled. The harness and wiring should be free of corrosion, abrasion, and pinch points. All connections and grounds should be tight and free of corrosion.
Results:
- OK - All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, abrasion, and pinch points. All connections and grounds are tight and free of corrosion. Proceed to Test Step 2.
- Not OK -
Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and that the connectors are completely coupled.Verify that the repair eliminates the problem.
Stop.
Test Step 2. Check the Solenoid for an Internal Short or Open.
- Disconnect power shift solenoid connector J113/P113.
- Measure the resistance between P113-1 and P113-2.
Expected Result:
The resistance should be between 7 Ohms and 17 Ohms.
Results:
- OK - The resistance is between 7 Ohms and 17 Ohms. Proceed to Test Step 3.
- Not OK - The resistance is not between 7 Ohms and 17 Ohms. The solenoid is faulty.
Repair: Replace the solenoid.Verify that the repair eliminates the problem.
Stop.
Test Step 3. Check the Resistance through the Harness.
- Disconnect ECM connector J2/P2.
- Use a suitable piece of wire to short P2-13 (Power Shift Solenoid) to P2-7 (Solenoid Return).
- Measure the resistance between J113-1 and J113-2.
- Remove the wire short.
Expected Result:
The resistance should be less than 10 Ohms.
Results:
- OK - The resistance is less than 10 Ohms. Proceed to Test Step 4.
- Not OK - The resistance is greater than 10 Ohms. There is an open circuit or there is excessive resistance in the harness.
Repair: Repair the circuit.Verify that the repair eliminates the problem.
Stop.
Test Step 4. Check for Shorts in the Harness.
- Turn the keyswitch to the OFF/RESET position.
- Disconnect ECM connector J2/P2 and power shift solenoid connector J113/P113.
- Measure the resistance between engine ground and each terminal of power shift solenoid connector J113.
- Measure the resistance between both terminals of power shift solenoid connector J113.
Expected Result:
The resistance should be greater than 20,000 Ohms for each reading.
Results:
- OK - The resistance is greater than 20,000 Ohms for each reading. Proceed to Test Step 5.
- Not OK - The resistance is less than 20,000 Ohms for each reading. There is a short in the harness between the ECM and the power shift solenoid.
Repair: Repair the circuit.Verify that the repair eliminates the problem.
Stop.
Test Step 5. Check the Voltage for the Solenoid at the ECM.
- Reconnect all connectors.
- Connect ET to the service tool connector.
- Start the engine.
- Ensure that the keyswitch is in the ON position.
- Check for any Active Diagnostic Codes.
Expected Result:
The following diagnostics should not be active:
- 581-05 "Power Shift Solenoid open circuit"
- 581-06 "Power Shift Solenoid short to ground"
Results:
- OK - The solenoid and the harness are OK.
Repair: If the system does not function properly refer to Troubleshooting, "Unstable Hydraulic Function".
Stop.
- Not OK - The ECM is faulty.
Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".Verify that the repair eliminates the problem.
Stop.