Cooling System Sensor Data Invalid

The engine control unit (ECU) expects a certain amount of coolant temperature readings but is getting nonsense values, meaning the engine might not be cooling properly.

The ECU monitors coolant temperature to adjust fuel delivery and ignition timing. If it doesn't receive a valid temperature reading (for example, 0°C or 150°C when normal is around 90°C), it sets this code.

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 condition of the wiring and connector to the coolant temperature sensor for wear or damage.
2. 22. Measure the voltage at the coolant temperature sensor connector with the ignition on (engine off). You should see around 5V (or the specific reference voltage for your vehicle). Decision: If voltage is absent, repair wiring or replace connectors as needed.
3. 33. Remove and inspect the coolant temperature sensor. Check for corrosion or damage. Decision: Replace the sensor if damaged.
4. 44. Use a scan tool to monitor the coolant temperature reading. Start the engine and confirm the reading rises steadily. Decision: If the reading is invalid or does not move (stays at 0 or 150°C when it shouldn’t), replace the sensor.
5. 55. Check engine coolant level. Low levels can cause erratic sensor readings. Decision: Refill the coolant and retest.

• Faulty coolant temperature sensor
• Wiring issues such as shorts or opens in the sensor harness
• Corrosion or poor connections at the sensor or the ECU
• Coolant leaks affecting sensor performance

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