SHEET 1038818 - Caterpillar

Use the Cat® Electronic Technician (Cat ET) Service Tool or the machine monitors to check for active diagnostic codes. If any diagnostic codes are present, refer to the appropriate diagnostic code troubleshooting procedure to correct this problem before continuing.Note: The procedure for setting main relief is specified in Testing and Adjusting, KENR9615. The main relief valve on the 374F have both a high setting and a low setting. A pilot signal to the main relief valve is used to switch between the high and low setting. The following procedure can be used to troubleshoot a suspected issue with main relief valve:
Adjust main relief using procedure in Testing and Adjusting, KENR9615. If achieving the proper setting of the main relief valve is not possible, follow these steps:
Verify pump 1 is stroking up during a "bucket stall" function through the monitor.
Verify pump 1 and 2 are stroking up during a "boom up stall" function through the monitor.
When adjusting the main relief high setting, if the setting does not change when the nut is adjusted, pilot oil is likely not being sent to main relief valve to activate high setting. If so follow the steps below:
Shut off the engine by turning the start switch to the OFF position. Ground implements and perform System Pressure Release procedure. Place volt meter leads on the solenoid that controls pilot signal to main relief valve, often referred to as the heavy lift solenoid valve. Use long leads to volt-meter to allow monitoring from a safe position.
With the machine running, monitor the voltage being supplied to the main relief control solenoid. If voltage is below 18V, troubleshoot the harness for shorts.
Shut off the engine by turning the start switch to the OFF position. Ground implements and perform System Pressure Release procedure. Measure resistance of main relief control solenoid. Resistance should be 32 3.2Ω. If resistance falls outside of specifications, replace the solenoid.
Plumb a pressure gauge to the pilot line connected to the main relief valve. Use a long hose to monitor the gauge pressure from a safe location.
With the machine running, monitor the pilot pressure sent to the main relief valve. If the pilot pressure falls outside of the range specified in Testing and Adjusting, KENR9615, "Relief Valve (Pilot) - Test and Adjust", use the procedure to adjust pilot pressure.
If pilot pressure was observed to be low in step 4.e above and pilot pressure upstream of the main relief control solenoid is within specifications, replace the main relief valve control solenoid. This solenoid is often referred to as the "heavy lift solenoid".
Perform bypass troubleshooting procedure to ensure bypasses are functioning properly
Replace the main relief, if the main relief has been replaced and the issue is still present, inspect the line reliefs.
Adjust or replace line relief for boom HE.