Engine Coolant Temperature Voltage High

The engine coolant temperature sensor is reporting temperatures that don't make sense, giving a higher voltage than it should when the engine is cold or at normal operating conditions.

The ECM sees a coolant temperature sensor voltage reading higher than the expected range, typically over 4.5 volts when it should be between 0.5 volts (cold) and 4.5 volts (hot).

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 11. Check the coolant level in the reservoir. If low, refill and check for leaks before proceeding. Decision: If coolant was low, monitor system; if not, continue.
2. 22. Inspect the wiring and connectors to the coolant temperature sensor for damage or corrosion. Decision: Repair any issues found, clear codes, and retest; if not, go to step 3.
3. 33. Measure the voltage at the coolant temperature sensor connector with the engine on and warmed up. Check for a reading of 1.5V-4.5V. Decision: If voltage is out of range, replace the sensor; if within range, follow step 4.
4. 44. Check the ground connection of the sensor. A poor ground can cause erroneous voltage readings. Decision: Repair any ground issues if found; if ground is good, continue to step 5.
5. 55. If all previous steps are good, consider testing or replacing the ECM.

• Wiring short to power
• Faulty coolant temperature sensor
• Poor ground connection
• Corroded connectors
• ECM issue

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