Caterpillar Excavator Fault Code 106: Complete Diagnostic Guide

What is Caterpillar Fault Code 106?

Caterpillar Fault Code 106 indicates an Engine Oil Pressure Sensor Circuit High Voltage condition, meaning the Electronic Control Module (ECM) has detected an abnormally high voltage signal from the oil pressure sensor circuit.

This diagnostic trouble code triggers when the ECM receives a voltage reading above the manufacturer's specified threshold (typically above 4.5-4.8 volts) from the engine oil pressure sensor. The oil pressure monitoring system is critical for Caterpillar excavators because it protects the engine from catastrophic damage by ensuring adequate lubrication to all moving components. When this fault is active, the ECM may enter a derate mode or trigger engine shutdown protocols to prevent damage, as it cannot reliably determine actual oil pressure levels.

Common Symptoms

When Code 106 is active, operators typically experience:

• Check Engine Warning Light illuminated on the instrument panel with possible oil pressure warning indicators
• Engine derate or reduced power output as the ECM enters a protective mode
• Erratic or maximum oil pressure gauge readings (pegged at highest reading) on the dashboard
• Engine shutdown in severe cases, particularly if the ECM cannot verify safe operating oil pressure
• Intermittent fault activation that may come and go, especially during machine vibration or temperature changes

Potential Causes

The most common technical causes for Code 106 on used Caterpillar excavators include:

• Open circuit in the oil pressure sensor wiring harness due to wire breakage or connector separation
• Failed oil pressure sensor with internal short circuit or deteriorated sensing element
• Corroded or damaged connectors at the sensor or ECM connection points (extremely common in older machines)
• Wiring harness chafing at known rub points near the engine block or chassis mounting locations
• ECM internal fault (rare) affecting the sensor input circuit
• Improper sensor installation or wrong sensor type after previous repairs on used equipment

How to Troubleshoot and Fix Code 106

Step 1: Visual Inspection Begin with a thorough inspection of the oil pressure sensor and its wiring harness. Check for obvious damage, oil contamination on connectors, corrosion at terminals, or wiring that shows signs of rubbing against engine components. On used excavators, pay special attention to harness routing near heat sources and vibration points where insulation commonly fails.

Step 2: Electrical Testing Using a digital multimeter, disconnect the oil pressure sensor connector and measure resistance across the sensor terminals. Compare readings against Caterpillar specifications (typically 50-300 ohms depending on model). Check for open circuits by measuring continuity from the sensor connector back to the ECM pins. Inspect for short-to-power conditions by measuring voltage at the disconnected sensor harness with key on, engine off (should read approximately 5 volts reference voltage).

Step 3: Sensor and Circuit Verification If wiring tests pass, replace the oil pressure sensor with a genuine Caterpillar part or quality equivalent. Before installation, clean connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Clear fault codes using Caterpillar Electronic Technician (CAT ET) software or compatible diagnostic tool and perform a test run. If the code returns, perform ECM input circuit testing or consult wiring diagrams for potential harness repair locations specific to your excavator model.

Disclaimer: This guide provides general diagnostic information. Complex electrical issues or ECM problems should be addressed by certified Caterpillar technicians with proper diagnostic equipment. Always consult your machine's service manual for model-specific procedures and specifications.