Engine shuts down or will not start; coolant temperature reading is implausible low or high; ECU logs coolant temp sensor fault.

Safety: Allow the engine to cool before touching coolant components. Hot coolant can cause burns.

• Locate sensor: The coolant temperature sensor is typically threaded into the cylinder head or thermostat housing on Volvo Penta industrial engines.
• Inspect connector: Disconnect the plug and check for corrosion, bent pins, or coolant intrusion. Clean with electrical contact cleaner and reconnect firmly.
• Check wiring continuity: Using a multimeter and wiring diagram, verify continuity from the sensor connector back to the ECU. Repair any open or shorted wires with proper splices.
• Test sensor resistance: Measure sensor resistance at ambient temperature and compare to Volvo Penta specifications. If out of range, replace the sensor with a genuine part and refill/bleed coolant if necessary.
• Recheck with diagnostics: Clear codes and monitor live coolant temperature readings. If the fault persists with a new sensor and good wiring, ECU input may be defective and requires professional evaluation.