What is Komatsu PC240LC-10 Fault Code E-28?

Fault Code E-28 on the Komatsu PC240LC-10 indicates a malfunction in the engine coolant temperature sensor circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage reading from the coolant temperature sensor, typically indicating an open circuit, short circuit, or sensor reading outside the expected range (generally -40°C to +150°C).

This code is critical because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, control engine warm-up procedures, and activate cooling fan operation. On the PC240LC-10's SAA6D107E-1 engine, incorrect temperature readings can lead to improper fuel mixture, reduced engine performance, and potential overheating damage. For used excavators, this sensor and its wiring are particularly vulnerable to environmental degradation and corrosion.

Common Symptoms

• Engine warning lamp illuminated on the monitor panel with E-28 displayed
• Hard starting or rough idling, especially during cold starts when ECM cannot adjust for actual temperature
• Cooling fan running continuously or not engaging at all, regardless of actual engine temperature
• Reduced engine power (derate mode) as the ECM enters a fail-safe operation using default temperature values
• Black or white exhaust smoke due to improper fuel-air mixture caused by inaccurate temperature compensation

Potential Causes

The most common technical failures triggering E-28 on used PC240LC-10 excavators include:

• Coolant temperature sensor failure – internal resistance element deterioration (common after 8,000+ hours)
• Damaged wiring harness – particularly at the sensor connector near the thermostat housing where heat and vibration cause wire insulation breakdown
• Corroded or loose connector pins at the sensor or ECM connection points (especially on machines operated in coastal or high-humidity environments)
• Open or short circuit in the sensor signal wire due to harness chafing against engine components
• ECM internal fault (rare) – damaged input channel on the control module itself

How to Troubleshoot and Fix Code E-28

Step 1: Visual Inspection Locate the coolant temperature sensor on the left side of the cylinder head near the thermostat housing. Inspect the sensor connector for corrosion, bent pins, moisture intrusion, or physical damage. Check the wiring harness from sensor to ECM for chafing points, particularly where it passes near the engine mount brackets – a known wear point on used PC240LC-10 models.

Step 2: Sensor Resistance Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At 20°C (68°F), resistance should read approximately 2,400-2,700 ohms. At 80°C (176°F), it should drop to approximately 300-330 ohms. Values outside this range confirm sensor failure requiring replacement (Komatsu part #6261-81-6510).

Step 3: Circuit Voltage Testing With the sensor disconnected and ignition on, measure voltage at the harness connector. You should see approximately 5 volts on the signal wire (reference voltage from ECM). If voltage is absent, trace the harness for breaks or check ECM connector integrity. Measure continuity to ground on the return wire – it should show less than 1 ohm resistance.

Step 4: Verification and Code Clearing After repairs, reconnect all components and use Komatsu KONTROL diagnostic software or a compatible scanner to clear the fault code. Run the engine through a full warm-up cycle while monitoring live coolant temperature data to confirm proper sensor operation and code resolution.

For used excavators, always apply dielectric grease to connector pins during reassembly to prevent future corrosion issues.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC240LC-10 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may void warranties or cause further damage.