What is Caterpillar Fault Code CID660?

CID660 indicates an Automatic Lubrication System (ALS) Pressure Switch Circuit malfunction on Caterpillar excavators. This diagnostic trouble code triggers when the Electronic Control Module (ECM) detects an abnormal voltage or signal from the automatic lubrication pressure switch, which monitors whether grease is being properly distributed to critical pivot points and pins throughout the machine.

This code is critical because the automatic lubrication system protects high-wear components like boom pins, bucket pins, and stick joints from premature failure. On used excavators, inadequate lubrication can accelerate wear exponentially, leading to costly repairs or catastrophic component failures. The system ensures continuous protection during operation, and when CID660 appears, the ECM cannot verify proper grease delivery to these vital areas.

Common Symptoms

• Amber warning light illuminated on the instrument cluster with "Check Engine" or lubrication system alert
• Audible alarm sounding intermittently or continuously when the machine is started
• Automatic lubrication system fails to cycle or distribute grease at programmed intervals
• Error message displayed on the monitor screen specifically referencing lubrication system fault
• Machine may continue operating normally, but long-term component wear accelerates without proper lubrication

Potential Causes

The most common technical reasons for CID660 on used Caterpillar excavators include:

• Pressure switch failure due to internal diaphragm wear or contamination from old grease buildup
• Wiring harness damage at known rub points near the lubrication pump mounting area or along the main frame rails
• Connector corrosion on the pressure switch harness connection, especially on machines exposed to wet or coastal environments
• Open or short circuit in the signal wire between the pressure switch and the ECM
• Low grease supply causing insufficient system pressure to activate the switch properly
• Failed lubrication pump preventing adequate pressure buildup in the distribution lines

How to Troubleshoot and Fix Code CID660

Step 1: Visual Inspection Locate the automatic lubrication pressure switch mounted on or near the grease pump assembly. Inspect the electrical connector for corrosion, bent pins, or moisture intrusion. On used excavators, check for harness chafing where wires route past frame members or hydraulic lines. Clean all connections with electrical contact cleaner.

Step 2: Electrical Testing Using a digital multimeter, disconnect the pressure switch connector and measure resistance across the switch terminals. Typical specifications range from 0-5 ohms when pressurized (refer to your service manual). Check for continuity in the harness from the switch back to the ECM connector. Measure voltage supply at the switch connector with ignition on (should read approximately 5-8 volts depending on model).

Step 3: Pressure and Component Verification Manually activate the lubrication system using Caterpillar Electronic Technician (Cat ET) diagnostic software. Monitor whether the system builds pressure and whether the switch responds. Inspect the grease reservoir level and check for blockages in distribution lines. On high-hour used machines, replace the pressure switch if readings are inconsistent, as internal components degrade over time.

Step 4: System Reset and Verification After repairs, clear the fault code using Cat ET software and cycle the lubrication system multiple times. Verify proper grease distribution at several lubrication points and confirm the code does not return.

---

Disclaimer: This guide provides general troubleshooting information. Always consult your Caterpillar service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.