Komatsu PC800-7 Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC800-7 Fault Code E-31?

Fault Code E-31 on the Komatsu PC800-7 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 outside the manufacturer's specified parameters, typically between 0.5-4.5 volts.

This fault is critical for the PC800-7's performance because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, engine protection protocols, and hydraulic system efficiency. When E-31 triggers, the engine may enter a protective derate mode to prevent overheating damage, significantly impacting productivity on job sites.

Common Symptoms

When Code E-31 is active, operators typically experience:

• Warning light illuminated on the instrument cluster, often accompanied by an audible alarm
• Engine derate or reduced power output, limiting hydraulic function speed and digging force
• Hard starting or rough idle, especially during cold starts when temperature compensation fails
• Erratic temperature gauge readings that fluctuate abnormally or remain at extreme values
• Increased fuel consumption due to improper fuel mapping from incorrect temperature data

Potential Causes

The most common technical reasons for E-31 on used PC800-7 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal element breakdown
• Wiring harness damage at known rub points near the engine block mounting brackets or along the chassis rail
• Corroded or loose connector pins at the sensor plug, especially on machines operating in coastal or high-humidity environments
• ECM internal circuit failure affecting the 5-volt reference supply to the sensor
• Coolant contamination causing sensor element coating or physical damage
• Aftermarket sensor incompatibility from previous repairs using non-OEM components

How to Troubleshoot and Fix Code E-31

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block's coolant passage. Check for physical damage, coolant leaks, or corrosion on the connector terminals. On used excavators, pay special attention to harness wear where wiring contacts metal surfaces or passes through grommets.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Next, check the wiring harness for continuity between the sensor connector and ECM pins. Verify the 5-volt reference signal from the ECM with the ignition on.

Step 3: Signal Testing Reconnect the sensor and use Komatsu diagnostic software (KOMTRAX) or a compatible scan tool to monitor live coolant temperature data. Compare readings against an infrared thermometer measurement of actual coolant temperature. A variance exceeding 10°F indicates sensor replacement is necessary.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu OEM sensor (Part #6732-81-3110 or equivalent). Clean connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Clear the fault code and perform a test cycle.

Disclaimer: This guide provides general diagnostic procedures. 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.