Prior to starting checks on the modulating valve for the torque converter lockup clutch, use Caterpillar ET in order to diagnose any fault codes that may be present. Refer to Systems Operation, Troubleshooting, Testing and Adjusting, RENR3442, "Power Train Electronic Control System".
Test the pressure of the oil in the torque converter lockup clutch. The torque converter lockup clutch can only be engaged on a stationary machine during a calibration of the retarder. Refer to Systems Operation, Testing and Adjusting, "Power Train Pressures" for the correct procedure to test the pressure in the torque converter lockup clutch. Inspect the area around the modulating valve for leakage.
The pressure test point for the torque converter lockup clutch is installed in the modulating valve for the torque converter lockup clutch. The modulating valve for the torque converter lockup clutch is located on the upper left side of the transmission.
If the pressure in the torque converter lockup clutch is insufficient, or there is no pressure in the torque converter lockup clutch, it will be necessary to check the operation of the solenoid coil.
Testing The Solenoid Coil Assembly
This test is carried out in order to determine if the solenoid coil on the modulating valve for the torque converter lockup clutch is energized.
Test for a rise in the pressure of the oil in the torque converter lockup clutch when the clutch is selected. Refer to Systems Operation, Testing and Adjusting, "Power Train Pressures".
If a pressure rise is noted, the solenoid and the related electrical circuit are functioning.
If a pressure rise is not noted, use a tag wire to check that the solenoid coil is energized. If the tag wire is attracted to the solenoid coil, this indicates that the solenoid coil is energized. The problem is in the solenoid cartridge. The problem could be a bent solenoid stem, a screen that is dirty or plugged, or a spring that is weak or broken.
If the tag wire does not indicate that the solenoid coil is energized, the problem is in the electrical circuit.
If the solenoid does not appear to function, disconnect the connector for the solenoid valve. Check the resistance of the windings of the coil in the solenoid.
The resistance of the windings in the solenoid should be 8.7Ohms ± 0.4Ohms.
If the resistance of the windings is outside the specifications replace the solenoid.
Reference: For additional information about the modulating valve for the torque converter lockup clutch, refer to Systems Operation, Testing and Adjusting, "Modulating Valves (Torque Converter Lockup Clutch)".