Komatsu PC800-7 Fault Code E931: Complete Diagnostic Guide

What is Komatsu PC800-7 Fault Code E931?

Fault Code E931 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically relates to the coolant temperature sensor sending irregular voltage signals or detecting temperatures outside the normal operating parameters for the SAA6D140E-5 engine.

This fault is critical for the PC800-7 because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, control engine protection systems, and prevent catastrophic overheating. When E931 triggers, the engine may enter a protective derate mode to prevent thermal damage, significantly impacting productivity on job sites.

Common Symptoms

When Code E931 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with reduced power output
• Engine derate or automatic shutdown if coolant temperature exceeds critical thresholds
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Difficulty starting in cold conditions due to incorrect fuel mapping
• Increased white smoke during startup if the ECM incorrectly assumes cold engine conditions

Potential Causes

The most common technical causes for E931 on used PC800-7 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal short circuits
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near engine block)
• Broken or frayed wires in the harness routing between the sensor and ECM, especially where harnesses contact frame rails
• Low coolant levels causing sensor exposure and false readings
• ECM internal fault (less common) affecting the temperature input circuit
• Aftermarket sensor installation with incorrect resistance specifications

How to Troubleshoot and Fix Code E931

Step 1: Visual Inspection Begin by checking coolant levels and inspecting the coolant temperature sensor located on the engine block's coolant passage. On used excavators, examine the connector for corrosion, moisture intrusion, or bent pins. Check the wiring harness routing for abrasion points, particularly where it passes near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult Komatsu specifications). Test harness continuity from sensor connector to ECM pins, checking for opens or shorts to ground. Measure supply voltage at the sensor connector with ignition on—should read approximately 5 volts.

Step 3: Component Replacement and Verification If resistance values are out of specification or harness damage is found, replace the faulty component using genuine Komatsu parts (part number 6732-81-3140 or equivalent). For used machines, always apply dielectric grease to connectors to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and perform a test cycle to verify repair.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC800-7 service manual and consider professional technician assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.