Komatsu D85PX-15 Fault Code E-5: Complete Diagnostic Guide

What is Komatsu D85PX-15 Fault Code E-5?

Fault Code E-5 on the Komatsu D85PX-15 bulldozer indicates a Transmission Oil Temperature Sensor Circuit malfunction. This code triggers when the machine's Electronic Control Module (ECM) detects abnormal voltage readings from the transmission oil temperature sensor, which monitors hydraulic fluid temperature in the torque converter and transmission system.

The transmission oil temperature sensor is critical for the D85PX-15's Hydrostatic Transmission (HST) system. This sensor provides real-time data that prevents overheating, protects internal clutch packs, and optimizes shifting performance. When the ECM cannot accurately read transmission temperature, it may force the machine into protective derate mode to prevent catastrophic transmission damage.

Common Symptoms

• Transmission warning light illuminated on the instrument panel (amber or red)
• Reduced engine power or speed limitation (derate mode activated around 1,400-1,600 RPM)
• Erratic transmission shifting or hesitation during direction changes
• Audible warning alarm sounding intermittently during operation
• Machine may operate normally at startup but trigger warnings after 15-30 minutes under load

Potential Causes

The E-5 code on used D85PX-15 machines typically stems from these issues:

• Damaged or corroded sensor connector (extremely common on machines with 5,000+ hours due to vibration and moisture intrusion)
• Failed transmission oil temperature sensor caused by prolonged exposure to heat cycling
• Wiring harness chafing near the transmission bellhousing where the harness routes along frame mounting points
• Contaminated transmission oil causing sensor element fouling or deposit buildup
• ECM internal fault (rare, but possible on machines manufactured before 2008)
• Loose or broken ground connections at the transmission case grounding points

How to Troubleshoot and Fix Code E-5

Step 1: Visual Inspection Locate the transmission oil temperature sensor on the right side of the transmission case (near the oil cooler inlet). Inspect the sensor connector for corrosion, bent pins, or moisture. On used excavators, check for harness abrasion where the wiring loom contacts the frame rail—a known wear point on this model.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 77°F (25°C), resistance should read approximately 2,200-2,800 Ω. Check harness continuity from the connector back to the ECM pin 47 (consult Komatsu service manual SEN05168-02). Verify supply voltage at the sensor connector with ignition on (should read 5V ±0.5V).

Step 3: Sensor and Fluid Verification Remove the sensor and inspect the probe tip for metallic debris or carbon deposits indicating contaminated oil. Check transmission oil condition—darkened or burnt-smelling fluid suggests overheating issues that may have damaged the sensor. Replace the sensor (Komatsu part #21W-04-21160) if resistance values are out of specification.

Step 4: Clear Code and Test After repairs, use Komatsu diagnostic software (KOMTRAX Plus) or a compatible J1939 diagnostic tool to clear the fault code. Operate the machine under load for 30 minutes while monitoring transmission temperature readings in real-time.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number. For used machines with complex electrical issues or persistent codes, professional diagnosis by a certified Komatsu technician is recommended to avoid unnecessary part replacement.