Komatsu PC120-6 Fault Code E-6: Complete Technical Guide

What is Komatsu PC120-6 Fault Code E-6?

Fault Code E-6 on the Komatsu PC120-6 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal temperature reading exceeding safe operating parameters. This code is triggered when the Electronic Control Module (ECM) detects either an open/short circuit in the coolant temperature sensor wiring or readings that fall outside the manufacturer's specified voltage range (typically 0.2-4.8V).

The coolant temperature sensor is critical for proper fuel injection timing, engine protection, and hydraulic oil temperature management on the PC120-6. When this sensor fails, the ECM cannot accurately monitor engine thermal conditions, potentially leading to overheating, reduced performance, or catastrophic engine damage if ignored.

Common Symptoms

• Warning light illuminated on the instrument panel (often a thermometer icon or check engine light)
• Engine power derate or limited RPM range, especially under heavy load conditions
• Difficulty starting when the engine is cold due to incorrect fuel delivery calculations
• Erratic temperature gauge readings or gauge stuck at full cold/hot positions
• Black smoke from exhaust due to improper fuel-air mixture from faulty temperature compensation

Potential Causes

The E-6 code on used PC120-6 excavators typically stems from age-related failures:

• Coolant temperature sensor degradation – internal thermistor failure after prolonged heat cycling
• Corroded or damaged wiring harness at connector pins, particularly where the harness runs near the engine block (known rub point on this model)
• Failed sensor ground connection due to rust accumulation on grounding terminals
• Coolant contamination causing sensor probe corrosion or mineral deposits affecting accuracy
• ECM internal circuit failure (rare, but possible on high-hour machines)

How to Troubleshoot and Fix Code E-6

Step 1: Visual Inspection
Inspect the coolant temperature sensor (located on the thermostat housing) and its two-wire connector. Check for cracked insulation, green corrosion on pins, or damaged connector seals. On used excavators, examine the wiring harness routing for wear points against engine components.

Step 2: Sensor Resistance Testing
Disconnect the sensor and measure resistance with a digital multimeter. At 20°C (68°F), resistance should read approximately 2.3-2.7 kΩ. At 80°C (176°F), expect around 0.3-0.4 kΩ. Values outside this range indicate sensor failure.

Step 3: Circuit Voltage Check
With ignition on and sensor connected, backprobe the signal wire (typically green/white). You should read 0.5-4.5V depending on temperature. A constant 5V indicates an open circuit; 0V suggests a short to ground.

Step 4: Wiring Harness Continuity
Test continuity between the sensor connector and ECM pins (consult service manual for exact pin numbers). Resistance should be less than 5Ω. Check for shorts to ground or power.

Step 5: Replacement and Verification
Install a genuine Komatsu coolant temperature sensor (Part #6732-81-3230 or equivalent). Clear codes using Komatsu diagnostic software (KOMTRAX) or by disconnecting the battery for 30 seconds. Test operation under normal conditions.

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Disclaimer: This guide provides general troubleshooting steps. Always consult the official Komatsu PC120-6 service manual and consider professional diagnostic assistance for complex electrical issues or if unfamiliar with excavator systems.