Komatsu D85PX-15 Fault Code E-24: Complete Diagnostic Guide

What is Komatsu D85PX-15 Fault Code E-24?

Fault Code E-24 on the Komatsu D85PX-15 bulldozer indicates a malfunction in the transmission oil temperature sensor circuit. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the transmission temperature sensor, typically caused by open circuits, short circuits, or sensor degradation.

The transmission oil temperature monitoring system is critical for the D85PX-15's powershift transmission protection. This sensor provides real-time data to the ECM, which adjusts shift patterns and activates protective derate modes when temperatures exceed safe operating thresholds. On used machines, this code often appears due to age-related sensor deterioration or wiring harness damage from heat cycling and vibration exposure.

Common Symptoms

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

• Warning lamp illumination on the instrument cluster (transmission caution light or master warning light)
• Erratic transmission behavior, including harsh shifts or unexpected gear changes
• Transmission derating where the ECM limits power output to prevent overheating damage
• Inaccurate temperature gauge readings or frozen temperature display on the monitor panel
• Intermittent code activation that appears and disappears, especially during cold starts or under heavy load

Potential Causes

The most common technical reasons for E-24 on used D85PX-15 machines include:

• Failed transmission oil temperature sensor due to internal thermistor degradation (common after 8,000+ operating hours)
• Damaged wiring harness at known rub points near the transmission bell housing where cables contact the frame
• Corroded or loose connector terminals at the sensor plug or ECM interface, especially on machines operated in wet/muddy conditions
• Shorted sensor wiring caused by insulation breakdown from prolonged heat exposure near the transmission case
• ECM internal circuit failure (rare, but possible on high-hour machines with previous electrical issues)
• Contaminated transmission oil causing sensor coating and inaccurate readings

How to Troubleshoot and Fix Code E-24

Step 1: Visual Inspection Begin by locating the transmission temperature sensor on the transmission case (typically on the left side, near the oil pan). Inspect the sensor connector for corrosion, oil contamination, or bent pins. On used excavators, check the wiring harness routing for chafing points where cables may contact metal surfaces or moving components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult Komatsu service manual for exact specifications). Check for continuity in the wiring between the sensor connector and ECM connector. Any reading of infinite resistance indicates an open circuit.

Step 3: Voltage Signal Verification With the sensor connected and ignition on (engine off), measure supply voltage at the sensor connector using your multimeter. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, suspect ECM issues or damaged harness wiring.

Step 4: Sensor Replacement and Harness Repair If testing confirms sensor failure, replace with a genuine Komatsu transmission temperature sensor (Part #: verify with dealer for D85PX-15 specific part number). For used machines with harness damage, repair damaged sections using heat-resistant wire rated for 250°F+ and apply dielectric grease to all connectors before reassembly.

Step 5: Clear Code and Verify After repairs, use Komatsu diagnostic software (KOMTRAX) or a compatible diagnostic scanner to clear the fault code. Operate the machine through warm-up cycles and monitor for code reoccurrence.

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Disclaimer: This guide provides general diagnostic information. Transmission system repairs should be performed by qualified technicians familiar with Komatsu equipment. Always consult the official Komatsu D85PX-15 service manual and follow lockout/tagout procedures before performing electrical diagnostics.