What is JCB Fault Code E718?

JCB Fault Code E718 indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor circuit, typically reading above 4.5-4.8 volts on JCB engines.

The ECT sensor is a critical component that monitors engine operating temperature and sends real-time data to the ECM. This information directly affects fuel injection timing, throttle response, and cooling fan operation. When E718 appears, the ECM cannot accurately determine engine temperature, which can lead to improper fuel delivery, overheating risks, and potential engine damage on used excavators where cooling system integrity may already be compromised.

Common Symptoms

• Engine warning light or malfunction indicator lamp (MIL) illuminated on the instrument cluster
• Engine running in limp mode or derate mode with significantly reduced power output
• Cooling fan running continuously at maximum speed, even during cold starts
• Difficulty starting when the engine is warm, or prolonged cranking periods
• Irregular idle quality or rough running due to incorrect fuel mapping based on false temperature readings

Potential Causes

The most common technical causes for E718 on used JCB excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire breakage or corrosion at connector points
• Failed or deteriorated coolant temperature sensor with internal resistance breakdown (common after 5,000+ operating hours)
• Damaged or corroded connectors at the sensor or ECM interface—particularly prone to moisture ingress on older machines
• Chafed or rubbed-through sensor wiring at known wear points near the engine block or along the frame rail
• Poor ground connection affecting sensor circuit reference voltage
• Rare ECM fault causing incorrect voltage supply to the sensor circuit

How to Troubleshoot and Fix Code E718

Step 1: Visual Inspection Inspect the ECT sensor connector and wiring harness for obvious damage, corrosion, or oil contamination. On used excavators, check for harness wear at movement points and heat-exposed areas near exhaust components.

Step 2: Sensor Resistance Test Disconnect the coolant temperature sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. Compare readings against JCB specifications (typically 2,000-3,000 ohms at 68°F/20°C). Readings showing infinite resistance or open circuit indicate sensor failure.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on (engine off), measure voltage at the ECM-side harness connector. You should see approximately 5 volts reference voltage. If voltage is absent or incorrect, trace wiring back to the ECM for breaks or shorts.

Step 4: Wiring Continuity Test Check continuity between the sensor connector and ECM pins using wiring diagrams. Test for short circuits to ground or power supply. Pay special attention to connector terminals for corrosion or bent pins common in high-hour machines.

Step 5: Component Replacement Replace the ECT sensor if testing confirms failure. Always use OEM or quality aftermarket parts. Clear codes with JCB Service Master diagnostic software and verify repair with a test run monitoring live data.

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Disclaimer: This guide provides general troubleshooting information. Always consult JCB service manuals and qualified diesel technicians for complex diagnostics. Improper repairs may cause further damage or safety hazards.