Komatsu D85EX-15 Fault Code E-24: Complete Diagnostic Guide

What is Komatsu D85EX-15 Fault Code E-24?

Fault Code E-24 on the Komatsu D85EX-15 bulldozer indicates a malfunction in the hydraulic oil temperature sensor circuit. This code triggers when the machine's Electronic Control Module (ECM) detects an abnormal voltage signal from the temperature sensor monitoring the hydraulic system's operating temperature.

The hydraulic oil temperature sensor is a critical component that allows the ECM to monitor fluid temperature and prevent overheating damage to pumps, motors, and seals. When this sensor fails or sends erratic signals, the D85EX-15 cannot accurately regulate hydraulic system performance, potentially leading to reduced efficiency or component damage. This fault is particularly important for used machines where sensor degradation and wiring deterioration are common.

Common Symptoms

When Code E-24 is active, operators typically experience:

• Warning lamp illumination on the instrument cluster, often accompanied by an audible alarm
• Inaccurate hydraulic temperature gauge readings or gauge stuck at minimum/maximum position
• Reduced hydraulic response as the ECM may enter a protective derate mode
• Intermittent fault activation during operation, especially when the machine vibrates or moves over rough terrain
• Error message display on digital monitor panels showing "Hydraulic Temp Sensor Error"

Potential Causes

The most common technical causes for Code E-24 on used D85EX-15 machines include:

• Failed hydraulic oil temperature sensor due to internal resistance drift or element burnout (common after 5,000+ operating hours)
• Damaged sensor wiring harness from abrasion against the hydraulic tank or frame rails—a known wear point on this model
• Corroded or loose electrical connectors at the sensor or ECM connection points, especially on machines operating in wet/salty environments
• Shorted sensor circuit caused by pinched wires near the hydraulic reservoir mounting brackets
• ECM internal fault (rare) affecting the sensor input circuit
• Contaminated connector terminals from hydraulic fluid leaks migrating along the wiring

How to Troubleshoot and Fix Code E-24

Step 1: Visual Inspection Begin by inspecting the hydraulic oil temperature sensor location on the hydraulic reservoir. Check for physical damage, oil contamination around the sensor base, and verify the wiring harness routing. On used excavators, pay special attention to areas where the harness contacts the frame—these are common abrasion points.

Step 2: Connector and Resistance Testing Disconnect the sensor connector and inspect terminals for corrosion, bent pins, or oil intrusion. Using a digital multimeter, measure sensor resistance across its terminals. Typical resistance values at 20°C should be 2,000-3,000 ohms (consult your specific service manual). Compare readings at different temperatures if possible.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on, measure voltage at the ECM-side harness connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or significantly different, suspect wiring issues or ECM problems.

Step 4: Wiring Continuity Test Check continuity between the sensor connector and ECM pins (refer to your D85EX-15 wiring diagram). Also test for shorts to ground. For used machinery, physically manipulate the harness while testing—intermittent connections often reveal themselves through fluctuating readings.

Step 5: Component Replacement If the sensor shows out-of-range resistance or the circuit tests reveal wiring damage, replace the faulty component. Always use genuine Komatsu parts or OEM-equivalent sensors to ensure proper ECM communication. After replacement, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool and verify repair with a test cycle.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu D85EX-15 service manual and consider professional technician assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.