Komatsu PC70-8 Fault Code E-6: Complete Diagnostic Guide

What is Komatsu PC70-8 Fault Code E-6?

Fault Code E-6 on the Komatsu PC70-8 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal temperature reading detected by the Engine Control Module (ECM). This code specifically relates to the coolant temperature sensor failing to provide accurate data or experiencing an electrical circuit fault.

The coolant temperature sensor plays a critical role in the PC70-8's engine management system. It monitors engine operating temperature and sends voltage signals to the ECM, which adjusts fuel injection timing, idle speed, and activates cooling fan operation. When this sensor fails or provides erratic readings, the ECM cannot properly regulate engine performance, potentially leading to overheating, poor fuel economy, or engine damage on used machines with accumulated wear.

Common Symptoms

When Code E-6 is active, operators typically experience:

• Warning light illuminated on the instrument panel (engine or temperature indicator)
• Engine running in limp mode or derated performance with reduced power output
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Difficulty starting when the engine is cold, or rough idle conditions
• Inaccurate temperature gauge readings (stuck at cold or hot positions)

Potential Causes

The most common technical reasons for E-6 on used PC70-8 excavators include:

• Coolant temperature sensor failure due to age, corrosion, or internal element degradation
• Wiring harness damage at known rub points near the engine block or cylinder head
• Corroded or loose connector pins at the sensor or ECM connection points
• Open or short circuit in the sensor signal wire or ground circuit
• ECM internal fault (less common, but possible in high-hour machines)
• Low coolant levels causing sensor exposure and false readings

How to Troubleshoot and Fix Code E-6

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically near the thermostat housing). Check for physical damage, coolant leaks, or corrosion on the connector terminals. On used excavators, examine the wiring harness for chafing, especially where it contacts metal surfaces or moves with engine vibration.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from sensor connector to ECM, checking for opens or shorts to ground.

Step 3: Signal Voltage Check With the ignition on and sensor connected, backprobe the signal wire. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent, trace the circuit back to the ECM connector for damaged pins or internal ECM issues.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu coolant temperature sensor. Clean all connector pins with electrical contact cleaner and apply dielectric grease to prevent future corrosion—critical for used machines operating in harsh environments.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu service manual for your specific serial number. If unfamiliar with electrical diagnostics, seek assistance from a certified heavy equipment technician to prevent further damage.