What is Yanmar DX75-9C Fault Code E001136-02?

Yanmar DX75-9C Fault Code E001136-02 indicates a voltage rationality fault on the engine coolant temperature (ECT) sensor circuit, specifically signaling that the sensor is outputting a signal that falls below the expected voltage threshold — commonly referred to as a "signal low" or "out of range low" condition.

This fault is managed by the Engine Control Module (ECM), which continuously monitors the ECT sensor to regulate fuel injection timing, cooling fan operation, and engine protection protocols. On the DX75-9C, an inaccurate coolant temperature reading can directly compromise engine thermal management, potentially leading to overheating events or improper fuel delivery — both serious concerns on any working excavator.

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Common Symptoms

When E001136-02 is active on your Yanmar DX75-9C, operators typically report:

• Warning indicator light illuminated on the instrument cluster
• Engine derate mode engaged, reducing power output and machine productivity
• Erratic or fixed temperature gauge reading (often pegged cold or showing no signal)
• Cooling fan running continuously at full speed as a failsafe response
• Difficulty with cold-start enrichment, causing rough idle or hard starting in low temperatures

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Potential Causes

The following are the most probable technical causes for this fault code:

• Failed or degraded ECT sensor — internal resistance drift is common on high-hour used machines
• Open circuit or broken wire in the sensor signal wire between the ECT sensor and ECM connector
• Corroded or loose connector pins at the sensor harness plug, particularly common in machines exposed to water ingress or pressure washing
• Chafed wiring harness where the engine harness routes near metal brackets or the engine block — a known wear point on compact excavators
• ECM connector corrosion causing loss of signal continuity at the control module end

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How to Troubleshoot and Fix Code E001136-02

Step 1 — Visual Inspection First Before testing any components, perform a thorough visual inspection. On used excavators, harness chafing, corrosion, and previous amateur repairs are the leading root causes. Inspect the ECT sensor connector, the harness routing along the engine block, and all ground points for signs of wear, melting, or moisture damage.

Step 2 — Check Sensor Resistance Disconnect the ECT sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. Cross-reference readings against the Yanmar DX75-9C specification chart (typically 2,000–3,000 ohms at 20°C / 68°F). A reading of infinite resistance (open circuit) confirms a failed sensor.

Step 3 — Test Circuit Continuity and Voltage With the ECM powered on (key-on, engine off), measure the reference voltage at the sensor harness connector using a multimeter. Expect approximately 5V reference voltage from the ECM. A reading of 0V indicates an open circuit or ECM output failure.

Step 4 — Inspect ECM Connector If wiring and sensor test normal, inspect the ECM harness connector for bent pins, corrosion, or moisture intrusion. Apply electrical contact cleaner and use a pin probe to verify continuity through each circuit wire.

Step 5 — Use Diagnostic Software Connect Yanmar's SmartAssist Remote or compatible dealer-level diagnostic software to read live sensor data and confirm ECT signal values in real time before condemning the ECM.

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Disclaimer: This guide is intended for informational purposes and general diagnostic direction only. Always consult a certified Yanmar dealer or licensed heavy equipment technician before performing repairs. Incorrect diagnosis or improper repairs on engine management systems can result in serious machine damage or safety hazards.