Cooling System Performance

The engine control unit (ECU) is not getting a normal coolant temperature signal from the temperature sensor, which means the engine might be overheating or running too cold.

The ECU expects the coolant temperature to be between 185°F and 210°F (85°C to 99°C) under normal operating conditions. If the signal from the coolant temp sensor is below 160°F (71°C) or above 230°F (110°C), this code is triggered.

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 coolant level and condition; ensure it is within the proper range. Decision point: If low, refill and retest. If proper, proceed to next step.
2. 22. Inspect the wiring and connectors at the coolant temperature sensor for damage or corrosion. Decision point: Repair any issues found or replace the wiring, then retest. If no issues, proceed to next step.
3. 33. Use a scan tool to read the actual coolant temperature value against the expected range. Decision point: If out of range (low or high), replace the coolant temperature sensor; if within range, check thermostat operation.
4. 44. Test the thermostat by observing coolant flow and temperature readings during engine warm-up. Decision point: If the thermostat is stuck, replace it. If it operates correctly, consider further diagnostics.
5. 55. Check for any engine overheating issues such as hose blockages or radiator issues, which might affect normal operation. Decision point: Resolve any issues found.

• Faulty coolant temperature sensor
• Wiring issues or bad connectors
• Low coolant level
• Thermostat stuck open/closed
• Engine overheating or running cold

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