Komatsu D85EX-15 Fault Code E-13: Complete Diagnostic Guide

What is Komatsu D85EX-15 Fault Code E-13?

Fault Code E-13 on the Komatsu D85EX-15 dozer indicates a transmission oil temperature sensor circuit malfunction. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the transmission oil temperature sensor, typically indicating an open circuit, short circuit, or sensor failure.

The transmission temperature monitoring system is critical for the D85EX-15's hydrostatic transmission performance. The ECM relies on accurate temperature data to adjust transmission response, prevent overheating, and protect internal components. When E-13 is active, the system may enter a protective derate mode, compromising productivity and potentially causing premature transmission wear if ignored.

Common Symptoms

• Transmission temperature warning light illuminated on the dash panel
• Reduced transmission responsiveness or sluggish blade/ripper operation
• ECM may default to engine speed limitation mode (typically around 1,800 RPM)
• Intermittent or constant fault code display on the monitor panel
• Transmission may feel like it's operating in "limp mode" with reduced power transfer
• Abnormal transmission noise or overheating despite actual normal operating temperatures

Potential Causes

On used D85EX-15 dozers, this code typically stems from age-related deterioration:

• Failed transmission oil temperature sensor (sensor element degradation is common after 8,000+ hours)
• Corroded or loose wiring connectors at the sensor harness junction near the transmission case
• Damaged sensor wiring harness from rubbing against the transmission housing or undercarriage components
• Contaminated sensor threads with metallic debris or old sealant affecting ground continuity
• ECM internal circuit failure (less common, but possible on high-hour machines)
• Low transmission oil level causing erratic temperature readings due to sensor exposure

How to Troubleshoot and Fix Code E-13

Step 1: Visual Inspection Locate the transmission oil temperature sensor on the left side of the transmission case. Inspect the wiring harness for obvious damage, chafing, or oil contamination. Check connector pins for corrosion or pushed-back terminals—common on used excavators exposed to harsh conditions.

Step 2: Sensor Resistance Test Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At approximately 68°F (20°C), resistance should read 2,200-2,800 ohms. Compare with warm transmission oil (around 140°F) where resistance should drop to 300-400 ohms. Values outside this range indicate sensor replacement is needed.

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. No voltage indicates a wiring break or ECM issue.

Step 4: Harness Continuity Test Check for continuity and shorts between the sensor wiring and chassis ground. Inspect particularly where harnesses route near sharp edges or moving components—a known wear point on D85EX models.

Step 5: Sensor Replacement and Verification If the sensor tests faulty, replace it with a genuine Komatsu part (P/N: 7861-93-3320 or equivalent). Apply anti-seize compound to threads and torque to 15-18 ft-lbs. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then operate the machine through temperature cycles to confirm repair.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu D85EX-15 service manual and consider professional assistance for complex electrical diagnostics or transmission repairs.