Komatsu PC220-7 Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC220-7 Fault Code E-31?

Fault Code E-31 on the Komatsu PC220-7 indicates a malfunction in the hydraulic oil temperature sensor circuit. This code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the temperature sensor monitoring the hydraulic system's oil temperature.

The hydraulic oil temperature sensor plays a critical role in protecting the PC220-7's hydraulic system. When hydraulic fluid exceeds safe operating temperatures (typically above 80-90°C), the sensor alerts the ECM to prevent damage to seals, hoses, and hydraulic components. On this excavator model, overheating can lead to reduced pump efficiency, accelerated component wear, and potential system failure. The ECM uses this data to trigger warning systems and, in severe cases, initiate derate modes to protect the machine.

Common Symptoms

When Code E-31 is active on your PC220-7, you may experience:

• Warning light illumination on the instrument cluster, specifically the hydraulic oil temperature indicator
• Erratic temperature gauge readings or gauge stuck at maximum/minimum positions
• Reduced hydraulic performance as the ECM may limit system pressure as a protective measure
• Intermittent alarms that appear and disappear, especially during temperature changes or machine vibration
• Derate mode activation in extreme cases, limiting engine RPM and hydraulic flow

Potential Causes

The most common causes of E-31 on used PC220-7 excavators include:

• Faulty hydraulic oil temperature sensor due to age-related failure or internal short/open circuits
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connection points near the hydraulic tank
• Loose or corroded electrical connectors at the sensor or ECM interface—common on machines with 5,000+ operating hours
• Chafed wiring where the harness contacts the frame or hydraulic lines during boom/arm movement
• ECM internal faults (rare) affecting the temperature sensor input circuit
• Contaminated hydraulic oil causing sensor element fouling or coating

How to Troubleshoot and Fix Code E-31

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically mounted on the return side). Inspect the wiring harness from sensor to ECM for obvious damage, chafing, or oil contamination. On used excavators, pay special attention to areas where the harness passes near moving components or sharp edges—a known wear point on PC220-7 models.

Step 2: Connector and Continuity Testing Disconnect the sensor connector and inspect for corrosion, bent pins, or oil intrusion. Clean contacts with electrical contact cleaner. Using a digital multimeter, check for continuity between the sensor connector and the ECM connector. Resistance should be less than 5 ohms. Check for shorts to ground (infinite resistance expected).

Step 3: Sensor Resistance Testing With the sensor disconnected, measure resistance across the sensor terminals. At ambient temperature (20°C), resistance should typically read between 2,000-3,000 ohms (consult your PC220-7 service manual for exact specifications). Compare readings at different temperatures if possible—resistance should decrease as temperature increases.

Step 4: Voltage Signal Testing Reconnect the sensor and back-probe the signal wire at the ECM connector with the ignition on. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, suspect ECM issues or power supply problems.

Step 5: Component Replacement If the sensor fails resistance testing or voltage signals are erratic, replace the hydraulic oil temperature sensor with a genuine Komatsu part (Part #7861-93-3320 or equivalent). After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool and test operation under load.

Disclaimer: This guide provides general troubleshooting information. Always consult your Komatsu PC220-7 service manual for model-specific procedures and specifications. For complex electrical diagnostics or if you're uncomfortable working with excavator systems, consult a certified Komatsu technician or qualified heavy equipment mechanic.