What is Caterpillar Fault Code 1145-6?

Caterpillar Fault Code 1145-6 indicates a short to ground condition in the Engine Coolant Temperature (ECT) Sensor circuit. Specifically, the ECM (Engine Control Module) has detected that the signal voltage from the coolant temperature sensor has dropped below the acceptable minimum threshold, suggesting the circuit is shorted to ground.

This fault is critical because the ECT sensor directly influences fuel injection timing, cooling fan engagement, and engine protection strategies. On used Caterpillar equipment, an unresolved 1145-6 can trigger aggressive engine derate or unexpected shutdowns to prevent catastrophic overheating damage.

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Common Symptoms

When fault code 1145-6 is active, operators typically experience:

• Warning lamp illuminated on the dashboard or monitor display
• Engine entering derate mode, reducing power and RPM output
• Inaccurate or pegged coolant temperature reading on the gauge (often reading maximum or zero)
• Automatic cooling fan running at full speed continuously
• Possible engine shutdown if the protection strategy interprets the fault as an overheating event

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Potential Causes

The most likely technical causes for this fault include:

• Damaged or chafed wiring harness — particularly common in used machines where harnesses have experienced years of vibration and rubbing against frame components
• Corroded or moisture-contaminated sensor connector — a frequent issue on older excavators exposed to harsh environments
• Failed ECT sensor with an internal short to ground
• Damaged ECM connector pins causing unintended ground contact
• Improper previous repairs where harness routing was not restored correctly

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How to Troubleshoot and Fix Code 1145-6

Step 1 — Inspect the Harness and Connector First On any used excavator, begin with a thorough visual inspection of the ECT sensor harness. Trace the wiring from the sensor back toward the ECM, looking for chafe points, melted insulation, or pinch damage near the engine block or frame rails. Check the connector for corrosion, bent pins, or moisture intrusion before touching any components.

Step 2 — Perform Voltage and Resistance Checks Disconnect the ECT sensor connector. Using a digital multimeter, measure resistance between the signal wire and ground. A healthy circuit should show no continuity to ground. If continuity exists, isolate whether the short is in the sensor itself or the wiring harness by testing each separately.

Step 3 — Use Cat ET Diagnostic Software Connect Caterpillar Electronic Technician (Cat ET) software to monitor live sensor data and confirm the fault is active with the sensor disconnected. If the code clears with the sensor unplugged, replace the ECT sensor. If the fault remains, the short exists within the wiring harness or ECM circuit.

Step 4 — Clear and Verify After repairs, clear the fault codes using Cat ET, perform a warm-up cycle, and confirm the coolant temperature reads accurately with no recurring faults.

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Disclaimer: This guide is intended for informational purposes and qualified technicians. Always consult a certified Caterpillar dealer or licensed heavy equipment mechanic before performing repairs, particularly on machines still under warranty or in critical operational service.