What is Caterpillar Fault Code CID4668?

CID 4668 indicates an abnormal voltage condition detected in the Engine Oil Pressure (EOP) sensor circuit. This Component Identifier (CID) code is logged when the Electronic Control Module (ECM) detects voltage readings outside the normal operating range from the oil pressure sensor, typically indicating either an open circuit, short to ground, or short to high voltage.

This fault code is critical for Caterpillar excavators because the ECM relies on accurate oil pressure data to protect the engine from catastrophic damage. When this sensor circuit malfunctions, the system cannot properly monitor lubrication system performance, potentially leading to engine derate or shutdown protocols to prevent bearing damage or complete engine failure. For used excavators, this code often appears due to age-related electrical degradation rather than actual oil system problems.

Common Symptoms

• Check Engine lamp illuminated on the instrument cluster with reduced engine power
• Engine derate mode activated, limiting machine performance to protect components
• Erratic or flat-lined oil pressure gauge readings on the display
• Possible engine shutdown if the ECM cannot verify safe operating oil pressure
• Diagnostic trouble codes stored in ECM memory alongside related oil system alerts

Potential Causes

The most common technical causes for CID 4668 in used Caterpillar excavators include:

• Failed Engine Oil Pressure sensor with internal circuit breakdown (common after 5,000+ operating hours)
• Damaged or corroded wiring harness connections at the sensor plug, especially where harnesses route near hot exhaust components
• Chafed wires at known rub points along the engine block where vibration causes insulation wear
• Corroded pins in the ECM connector due to moisture infiltration in older machines
• Failed ECM (rare, but possible in high-hour machines with electrical system history)
• Improper sensor installation after previous maintenance causing intermittent connection issues

How to Troubleshoot and Fix Code CID4668

Step 1: Visual Inspection Begin by inspecting the oil pressure sensor located on the engine block and its wiring harness. Check for obvious damage, oil contamination on connectors, corroded terminals, or worn insulation. On used excavators, pay special attention to harness routing where friction against frame components commonly occurs.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across sensor terminals according to Caterpillar specifications (typically 50-250 ohms at room temperature). Check for voltage supply at the harness connector—should read approximately 5 volts with key on, engine off. Test for continuity between sensor ground and chassis ground.

Step 3: Sensor and Harness Verification Install Caterpillar Electronic Technician (ET) diagnostic software to monitor live oil pressure sensor voltage while wiggling harness connections. Voltage fluctuations indicate intermittent connection problems. Verify actual oil pressure using a mechanical gauge before replacing sensors—many used excavators have functional sensors with only wiring issues.

Step 4: Repair or Replace Replace damaged connectors or repair chafed wiring with heat-shrink terminals and protective loom. If the sensor tests faulty, install genuine Caterpillar replacement parts to ensure proper ECM communication. Clear codes and perform operational testing under load.

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