Komatsu PC35MR-2 Fault Code E-5: Complete Diagnostic Guide

What is Komatsu PC35MR-2 Fault Code E-5?

Fault Code E-5 on the Komatsu PC35MR-2 indicates a malfunction in the engine coolant temperature sensor circuit. This diagnostic trouble code signals that the Engine Control Module (ECM) has detected an abnormal voltage reading from the coolant temperature sensor, which could indicate sensor failure, wiring issues, or coolant system problems.

The coolant temperature sensor is critical for this compact excavator's performance because it directly affects fuel injection timing, engine warm-up protocols, and prevents overheating damage. When the ECM cannot accurately read engine temperature, it defaults to safe mode parameters that may reduce machine efficiency and power output. For used PC35MR-2 models, this code frequently appears due to age-related sensor degradation or corroded electrical connections.

Common Symptoms

When Code E-5 is active on your Komatsu PC35MR-2, operators typically experience:

• Engine warning light illuminated on the instrument panel (often steady or flashing)
• Hard starting when the engine is cold, or prolonged cranking periods
• Rough idle or irregular engine performance during warm-up phase
• Reduced engine power or inability to reach full RPM under load
• Black smoke from the exhaust due to incorrect fuel mixture calculations

Potential Causes

For the PC35MR-2, especially in used excavators, the most common causes include:

• Faulty coolant temperature sensor - internal resistance drift or complete sensor failure (common after 3,000+ operating hours)
• Damaged wiring harness - particularly where the sensor harness routes near the engine block, experiencing heat cycling and vibration
• Corroded or loose connector pins at the sensor plug (frequent in machines exposed to wet conditions)
• Low coolant level causing sensor exposure to air instead of coolant
• ECM internal fault (rare, but possible in high-hour machines with electrical system history)
• Grounding issues where the sensor ground circuit has developed high resistance

How to Troubleshoot and Fix Code E-5

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and overflow tank. Inspect the coolant temperature sensor (located on the engine block near the thermostat housing) for physical damage, coolant leaks, or corrosion. On used excavators, carefully examine the wiring harness for chafing, melted insulation, or pinch points where the harness contacts the engine.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 68°F (20°C), the sensor should typically read 2,000-3,000 ohms (consult your specific service manual for exact specifications). Next, check the voltage supply at the harness connector with the ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Harness and Ground Circuit Verification Inspect the connector pins for corrosion or bent terminals—this is extremely common in older machines. Test continuity from the sensor connector back to the ECM pins, and verify the ground circuit has less than 1 ohm resistance. For used excavators with high hours, consider applying dielectric grease to connections after cleaning.

Step 4: Component Replacement and Code Clearing If testing confirms sensor failure, replace with a genuine Komatsu sensor or OEM-equivalent part. After replacement, use Komatsu diagnostic software or a compatible scan tool to clear the fault code and monitor live data during a test run to confirm proper temperature readings (gradual increase from ambient to operating temperature around 180-200°F).

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC35MR-2 service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic equipment.