What is Komatsu D85PX-15 Fault Code E-19?

Fault Code E-19 on the Komatsu D85PX-15 bulldozer indicates a malfunction in the transmission oil temperature sensor circuit. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the transmission temperature sensor, suggesting either an open circuit, short circuit, or sensor failure.

The transmission oil temperature monitoring system is critical for the D85PX-15's Hydraulic Shift Transmission (HST) operation. This sensor continuously feeds data to the ECM, which uses it to regulate shifting patterns, torque converter lockup, and transmission protection protocols. When E-19 activates, the ECM may default to conservative operational parameters to prevent transmission damage, potentially limiting machine productivity and efficiency on jobsites.

Common Symptoms

When Code E-19 is active on your D85PX-15, operators typically experience:

• Warning light illumination on the instrument cluster, often accompanied by an audible alarm
• Derated transmission performance with hesitant or delayed shifting between gears
• Default temperature readings displayed on the monitor (often showing minimum or maximum values rather than actual temperature)
• Reduced torque converter efficiency, causing sluggish response under load
• ECM logging the fault in memory, even if symptoms are intermittent

Potential Causes

The most common technical reasons for E-19 activation on used D85PX-15 dozers include:

• Transmission temperature sensor failure due to age-related degradation or thermal cycling stress
• Damaged wiring harness near the transmission housing where vibration and heat cause wire insulation breakdown
• Corroded or loose connector pins at the sensor plug, especially on machines operated in wet or corrosive environments
• ECM internal circuit fault (less common but possible on high-hour units)
• Harness chafing against the transmission case or frame components, creating intermittent shorts
• Contaminated transmission oil causing sensor element fouling (check oil condition during diagnosis)

How to Troubleshoot and Fix Code E-19

Step 1: Visual Inspection Begin by locating the transmission oil temperature sensor on the right side of the transmission case. Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, this connector frequently shows green corrosion—clean with electrical contact cleaner and apply dielectric grease before reconnecting.

Step 2: Harness Continuity Check Disconnect the sensor and use a digital multimeter to check wiring continuity from the sensor connector back to the ECM. The D85PX-15 typically uses a two-wire sensor configuration (signal and ground). Check for 0-2 ohms resistance on both wires. Inspect harness routing for wear points against metal edges, especially where the harness passes near the transmission mounting points.

Step 3: Sensor Resistance Testing With the sensor removed, measure its resistance across the terminals. At room temperature (68°F/20°C), resistance should typically read 2,000-3,000 ohms (consult Komatsu service manual for exact specifications). If readings are infinite (open) or near zero (shorted), replace the sensor.

Step 4: Voltage Supply Verification Using Komatsu diagnostic software (KOMTRAX Plus) or a compatible scan tool, monitor live sensor voltage while the engine runs. Normal operating voltage should range 0.5-4.5 volts depending on temperature. Fixed readings at 0V or 5V indicate circuit faults rather than sensor issues.

Step 5: Connector and Ground Testing For used machinery, verify the ground circuit integrity by checking voltage drop between the sensor ground pin and battery negative—should be less than 0.1V. Poor grounding is a frequent culprit on older Komatsu machines.

Critical Note for Used Equipment: Before replacing the temperature sensor (Part# typically 7861-93-3320), thoroughly inspect the transmission oil condition. Metal contamination or burnt oil may indicate deeper transmission issues that caused sensor failure. Address root causes to prevent repeat failures.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu D85PX-15 service manual and consider professional diagnostic assistance for complex electrical issues. Improper troubleshooting may cause additional damage or safety hazards.