Engine Coolant Temperature Sensor Voltage Too High
The engine's coolant temperature sensor is sending a voltage signal that exceeds the acceptable limit.
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What it means (plain English)
The coolant temperature sensor tells the engine computer how hot the engine's coolant is. If it sends a voltage that’s too high, the computer thinks there’s a problem and might prevent proper engine performance.
What the computer is actually seeing
The engine control module (ECM) expects a voltage signal from the coolant temperature sensor to be within a range of about 0.5 to 4.5 volts, depending on the temperature. Voltages greater than 4.5 volts usually trigger this fault code.
What a healthy reading looks like
At operating temperature, the expected voltage is typically around 2.5 to 3.5 volts. Readings above 4.5 volts indicate an issue.
Guided diagnostic — the DiagCoach way
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.
- 11. Check the wiring and connector for the coolant temperature sensor for damage or corrosion. Repair as needed. If the connector is good, proceed to the next step.
- 22. Measure the voltage at the coolant temperature sensor with the engine running. If the voltage is above 4.5 volts, go to step 3. If it's normal, the fault may be intermittent; monitor the vehicle for recurrences.
- 33. Disconnect the sensor harness and measure the resistance of the sensor. If the resistance is out of spec (usually around 2,000 to 3,000 ohms at room temperature), replace the coolant temperature sensor.
- 44. If the sensor checks out, inspect the wiring from the sensor to the ECM for shorts that might cause high voltage readings. Repair any shorts found.
Common causes
- Shorted wiring in the coolant temperature sensor circuit.
- Faulty coolant temperature sensor.
- Corroded or loose connectors at the sensor or ECM.,
Typical repair cost
$$$
Related codes
Frequently asked questions
Why does this code sometimes appear with SPN 741?
SPN 741 is for a low coolant temperature signal. If both codes appear, it may indicate issues with the coolant temperature sensor or its wiring.
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