Komatsu D85EX-15 Fault Code E-19: Complete Diagnostic Guide

What is Komatsu D85EX-15 Fault Code E-19?

Fault Code E-19 on the Komatsu D85EX-15 bulldozer indicates a malfunction in the transmission oil temperature sensor circuit. This code triggers when the Engine Control Module (ECM) detects abnormal voltage readings from the transmission temperature sensor, signaling either an open circuit, short circuit, or implausible temperature values.

This code is critical for the D85EX-15's performance because the transmission oil temperature directly affects shift quality, hydraulic pressure regulation, and component longevity. The ECM uses this data to protect the transmission from overheating damage and optimize torque converter lockup timing. Ignoring this fault can lead to transmission overheating, premature clutch wear, or catastrophic transmission failure on used machines with existing wear.

Common Symptoms

Operators may experience the following when Code E-19 is active:

• Transmission warning light illuminated on the dashboard or monitor panel
• Harsh or delayed shifting between gears due to ECM entering protective mode
• Reduced machine performance with power limitations to prevent transmission damage
• Abnormal temperature gauge readings showing either maximum heat or no reading at all
• Audible warning alarm on some D85EX-15 configurations when fault is detected

Potential Causes

The most common technical causes for E-19 on used D85EX-15 dozers include:

• Faulty transmission oil temperature sensor due to age-related degradation or thermal cycling stress
• Damaged sensor wiring harness from rubbing against the transmission housing or frame rails (common wear point near the sensor mounting location)
• Corroded or loose electrical connectors at the sensor or ECM connection points, especially on machines operating in wet or coastal environments
• Short circuit to ground caused by chafed wiring insulation from vibration or improper previous repairs
• ECM internal fault (rare) affecting the sensor input circuit or reference voltage supply
• Contaminated transmission oil causing sensor element failure or coating that affects readings

How to Troubleshoot and Fix Code E-19

Step 1: Visual Inspection Begin by locating the transmission oil temperature sensor on the transmission case (typically on the left side near the filter housing). Inspect the wiring harness for obvious damage, chafing, or wear points where it contacts metal surfaces. On used excavators, check for previous repair attempts like electrical tape or spliced wires. Examine the electrical connector for corrosion, bent pins, or oil contamination.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At ambient temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from the sensor connector back to the ECM connector. Check for shorts to ground by measuring resistance between each sensor wire and chassis ground (should read infinite/open circuit).

Step 3: Sensor and Voltage Verification With the ignition on but engine off, measure the reference voltage at the sensor connector from the ECM (typically 5 volts). If voltage is absent or incorrect, trace the harness for breaks or check ECM pin connections. For used machines, physically remove the sensor and inspect for carbon buildup, damaged threads, or element damage. Replace the sensor if resistance values are out of specification or physical damage is evident.

Step 4: System Reset and Verification After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and operate the machine through several temperature cycles. Monitor live data to ensure the temperature sensor provides smooth, realistic readings from cold startup through operating temperature (typically 180-220°F).

Disclaimer: This guide provides general diagnostic information for the Komatsu D85EX-15. Always consult the official Komatsu service manual for your specific serial number and model year. If you lack proper diagnostic tools or experience, contact a certified Komatsu technician to prevent misdiagnosis or additional damage.