What is Komatsu PC120LC-6 Fault Code E-6?

Fault Code E-6 on the Komatsu PC120LC-6 indicates an Engine Overheat Condition detected by the electronic monitoring system. This code triggers when the engine coolant temperature sensor reports values exceeding the safe operating threshold, typically above 105-110°C (221-230°F), signaling the Engine Control Module (ECM) to activate protection protocols.

This fault is critical for the PC120LC-6's SAA6D102E engine because sustained overheating causes cylinder head warping, head gasket failure, and potential catastrophic damage to pistons and bearings. The system is designed to derate engine power or initiate shutdown to prevent irreversible damage. In used excavators, this code often reveals accumulated wear in the cooling system or sensor degradation common in machines with 6,000+ operating hours.

Common Symptoms

• Engine warning lamp illuminates continuously or flashes on the instrument panel
• Automatic engine power derate reducing hydraulic performance and digging force by 30-40%
• Coolant temperature gauge reading in the red zone (above 100°C)
• Audible alarm sounding from the cab, typically a continuous beep pattern
• White steam or vapor venting from the radiator or overflow tank during operation

Potential Causes

For the PC120LC-6, particularly in used machinery, common causes include:

• Coolant temperature sensor failure – The sensor (part #6732-81-6210) develops internal resistance drift, sending false high-temperature signals
• Clogged radiator core – Mud, debris, and hydraulic oil contamination blocking airflow, common in machines operating in dusty/muddy conditions
• Failed thermostat – Stuck-closed thermostat preventing coolant circulation through the radiator
• Degraded coolant – Loss of coolant properties due to infrequent service intervals (should be replaced every 2,000 hours)
• Water pump bearing failure – Worn impeller or bearing causing inadequate coolant flow
• Wiring harness damage – Sensor wire chafing near the engine block mounting point, creating intermittent short circuits

How to Troubleshoot and Fix Code E-6

Step 1: Verify Actual Temperature Use an infrared thermometer to measure actual coolant temperature at the thermostat housing. If reading shows 80-95°C but code persists, suspect sensor failure rather than true overheating.

Step 2: Test Coolant Temperature Sensor Disconnect the 2-pin sensor connector located on the cylinder head's front-left side. Using a digital multimeter, measure resistance: it should read 200-300 ohms at 80°C. Values outside this range require sensor replacement (OEM part #6732-81-6210).

Step 3: Inspect Physical Cooling System Check radiator fins for blockage—pressure-wash from engine side outward. Verify coolant level in overflow tank and test coolant concentration with a refractometer (should be 50/50 mix). Inspect drive belts for proper tension (13mm deflection under 10kg pressure).

Step 4: Check Wiring Harness For used excavators, carefully inspect sensor wiring where it routes along the valve cover. Look for insulation wear, bare copper, or corrosion at connector terminals. Repair or replace damaged sections with heat-shrink sealed connectors.

Step 5: Clear Code and Test After repairs, use Komatsu KOMTRAX diagnostic software or compatible scan tool to clear fault codes. Monitor temperature during a 30-minute operational test under load.

---

Disclaimer: This guide provides general diagnostic information. Always consult certified Komatsu technicians or authorized service manuals for complex repairs. Improper diagnosis may lead to equipment damage or safety hazards.