Caterpillar Excavator Fault Code 107-15: Complete Diagnostic Guide

What is Caterpillar Fault Code 107-15?

Caterpillar Fault Code 107-15 indicates a "Fuel Pressure Sensor Circuit - Voltage Above Normal or Shorted to High Source." This diagnostic trouble code (DTC) means the Electronic Control Module (ECM) has detected an abnormally high voltage reading from the fuel rail pressure sensor, typically exceeding 4.8-5.0 volts when normal operating range should be 0.5-4.5 volts.

This fault directly impacts the ECM's ability to manage fuel injection timing and pressure regulation in Caterpillar's common rail fuel systems. When the ECM cannot accurately read fuel pressure, it cannot optimize combustion efficiency, leading to performance degradation and potential engine protection modes. For used excavators, this code often signals age-related electrical issues rather than actual fuel system failures.

Common Symptoms

When Code 107-15 is active, operators typically experience:

• Check Engine Light or malfunction indicator lamp illuminated on the dash
• Engine derate or power reduction mode (typically 25-40% power loss)
• Hard starting or extended cranking periods, especially when cold
• Rough idling or inconsistent RPM fluctuation at low speeds
• Black smoke from exhaust due to improper fuel metering
• Possible fuel consumption increase as ECM defaults to safe-mode fueling parameters

Potential Causes

The most common technical causes for Code 107-15 in used Caterpillar excavators include:

• Damaged sensor wiring harness - particularly at flex points near the engine block where vibration causes wire insulation breakdown
• Corroded or moisture-contaminated connectors at the fuel pressure sensor (3-pin Deutsch connector)
• Shorted sensor signal wire to battery voltage (+12V or +24V depending on system)
• Failed fuel rail pressure sensor with internal circuit short (less common than wiring issues)
• Chafed wiring rubbing against engine components, valve covers, or fuel lines
• ECM pin corrosion at the sensor input terminals
• Aftermarket harness repairs using incorrect wire gauge or inadequate insulation

How to Troubleshoot and Fix Code 107-15

Step 1: Visual Inspection Begin with a thorough inspection of the fuel pressure sensor and its wiring harness. On used excavators, focus on known wear points: where the harness passes over the valve cover, near exhaust manifolds, and at the sensor connector itself. Look for melted insulation, green corrosion on copper wires, or oil-soaked connectors that indicate seal failure.

Step 2: Connector and Resistance Testing Disconnect the 3-pin sensor connector and inspect for bent pins, moisture, or corrosion. Using a digital multimeter, check sensor resistance between the signal pin and ground (typically 100-300 ohms at 68°F). Then measure harness resistance from the ECM connector to the sensor plug—readings above 5 ohms indicate wire degradation.

Step 3: Voltage Circuit Testing With ignition ON and sensor disconnected, measure voltage at the 5-volt reference wire (should read 4.9-5.1V). Check the signal wire for voltage—any reading above 0.3V indicates a short to power source. Inspect the harness routing for contact points with positive battery cables or starter solenoid wiring.

Step 4: Sensor Replacement vs. Harness Repair If wiring tests pass, replace the fuel rail pressure sensor (Caterpillar part number varies by engine model—consult service manual). For used machines with harness damage, repair using OEM-spec 18-gauge wire with proper heat-shrink sealing, or replace the entire engine harness section if multiple codes exist.

Step 5: Clear Codes and Verify After repairs, clear fault codes using Caterpillar Electronic Technician (Cat ET) diagnostic software and run the engine through various load conditions. Monitor live fuel pressure data (should range 3,000-29,000 PSI depending on load) to confirm proper sensor operation.

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Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the specific Caterpillar service manual for your excavator model and consider professional diagnosis if unfamiliar with high-pressure fuel systems or electrical diagnostics.