Komatsu PC220-10 Fault Code E-27: Complete Diagnostic Guide

What is Komatsu PC220-10 Fault Code E-27?

Fault Code E-27 on the Komatsu PC220-10 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal temperature reading detected by the Engine Control Module (ECM). This code typically signals that the coolant temperature sensor is either sending erratic voltage signals, experiencing an open or short circuit, or detecting engine temperatures outside the normal operating range (typically -40°C to 150°C).

The coolant temperature sensor is critical for the PC220-10's SAA6D107E-1 engine performance. The ECM relies on accurate temperature data to control fuel injection timing, regulate engine speed, and protect the engine from overheating. When E-27 triggers, the ECM may default to fail-safe mode, compromising machine efficiency and potentially causing engine damage if ignored.

Common Symptoms

When Code E-27 is active, operators typically experience:

• Check engine warning light illuminated on the monitor panel
• Engine derate or limited power output as the ECM enters protective mode
• Hard starting or rough idling, especially during cold starts
• Inaccurate temperature gauge readings on the dashboard display
• Cooling fan running continuously at high speed regardless of actual engine temperature

Potential Causes

The most common technical reasons for E-27 on used PC220-10 excavators include:

• Faulty coolant temperature sensor – Internal sensor degradation is common after 5,000+ operating hours
• Damaged wiring harness – Rubbing against engine components near the thermostat housing causes insulation wear
• Corroded electrical connectors – Moisture intrusion at the sensor connector (common pinch point on this model)
• Low coolant level – Exposes the sensor tip, causing false readings
• ECM calibration issues – Rare, but previous software updates may conflict with sensor parameters
• Thermostat failure – Can cause actual overheating that triggers the code legitimately

How to Troubleshoot and Fix Code E-27

Step 1: Visual Inspection Using the Komatsu diagnostic port (located under the cab floor), connect KOMTRAX software or a compatible scan tool to verify the active code. Check the actual coolant level and inspect the sensor connector near the thermostat housing for corrosion, pushed-out pins, or moisture. On used excavators, this connector often shows green corrosion from coolant leaks.

Step 2: Electrical Testing Disconnect the two-wire coolant temperature sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. At 20°C (68°F), resistance should read approximately 2,400-2,700 Ohms (consult your service manual for exact specifications). Check for continuity to ground on both wires with the harness disconnected from the ECM – any continuity indicates a short circuit.

Step 3: Harness and ECM Verification Inspect the wiring from the sensor to the ECM (located behind the operator seat) for chafing, particularly where the harness passes near the engine mount bracket. Measure reference voltage from the ECM at the harness connector – should be approximately 5 volts DC. If voltage is absent, suspect ECM issues or a blown fuse in the sensor circuit.

Step 4: Component Replacement If testing confirms sensor failure, replace with genuine Komatsu part number 6754-85-3140 or equivalent. Apply dielectric grease to connector terminals before reassembly. Clear codes using diagnostic software and run the engine through a full heat cycle to verify repair.

Critical for Used Machines: Before replacing the sensor, always check for coolant contamination in the connector and verify the thermostat opens correctly (typically at 82°C). Many E-27 codes on high-hour machines result from poor-quality coolant causing sensor coating buildup rather than actual sensor failure.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC220-10 service manual and consider professional evaluation for complex electrical issues or if you're unfamiliar with high-voltage systems. Improper diagnostics can lead to costly misdiagnosis or safety hazards.