What is Komatsu PC110-7 Fault Code E-21?

Komatsu PC110-7 Fault Code E-21 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal engine coolant temperature reading. This code is triggered when the Engine Control Module (ECM) detects a voltage signal from the coolant temperature sensor that is outside the expected range, or when the sensor fails to communicate proper temperature data.

The coolant temperature sensor is a critical component in the PC110-7's engine management system. It monitors engine operating temperature and sends voltage signals to the ECM, which then adjusts fuel injection timing, idle speed, and activates the cooling fan. On used excavators, this sensor's accuracy is vital for preventing engine overheating, maintaining optimal fuel efficiency, and ensuring proper hydraulic oil temperature for component longevity.

Common Symptoms

When Code E-21 is active on your Komatsu PC110-7, you may experience:

• Engine warning light illuminated on the instrument panel (typically amber or red)
• Cooling fan running continuously at high speed, even when engine is cold
• Difficulty starting the engine, especially in cold weather conditions
• Engine derate mode activated, limiting maximum RPM and hydraulic performance
• Erratic temperature gauge readings or gauge stuck at minimum/maximum position

Potential Causes

The most common technical causes for E-21 on used PC110-7 excavators include:

• Failed coolant temperature sensor due to internal resistance drift (common after 5,000+ operating hours)
• Damaged wiring harness near the thermostat housing where vibration causes wire chafing
• Corroded or loose electrical connectors at the sensor or ECM (especially on machines exposed to wet conditions)
• Shorted or open circuit in the sensor signal wire between sensor and ECM
• Contaminated coolant causing sensor tip fouling or corrosion
• Faulty ECM (less common, but possible on high-hour machines)

How to Troubleshoot and Fix Code E-21

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks, or corrosion on the connector terminals. On used excavators, examine the wiring harness for signs of rubbing against the engine block or heat damage from the exhaust manifold.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's resistance. With the engine cold, resistance should typically read 2,000-3,000 ohms (verify exact specifications in your service manual). Check voltage supply at the connector—you should see approximately 5 volts reference voltage from the ECM. Inspect for continuity in the signal wire back to the ECM.

Step 3: Component Replacement and Verification If resistance values are out of specification or the connector shows corrosion (common in used machines), replace the coolant temperature sensor using a genuine Komatsu part. Clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible tool) and monitor during a complete warm-up cycle. For persistent codes, inspect ECM connections and consider professional ECM testing.

Disclaimer: This guide provides general troubleshooting information. Always consult your Komatsu PC110-7 service manual for exact specifications and safety procedures. If you're uncomfortable with electrical diagnostics, seek assistance from a certified Komatsu technician.