Engine Coolant Temperature Sensor 1 - Voltage Above Normal, or Shorted to High Source
The engine coolant temperature sensor is reporting a voltage that is too high, indicating a possible issue with the sensor or wiring.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The computer reads the coolant temperature from a sensor. If that voltage goes above about 4.9 volts, it thinks there's a problem, and it might not know how hot the engine really is, which can lead to overheating.
What the computer is actually seeing
The ECM is monitoring the engine coolant temperature sensor, expecting a voltage between approximately 0.5 volts (cold engine) to 4.5 volts (hot engine). If it sees a voltage above 4.9 volts, it triggers the fault code.
What a healthy reading looks like
Expected sensor signal voltage should be between 0.5 and 4.5 volts at normal operating temperature.
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 wiring and connectors to the engine coolant temperature sensor for damage or corrosion.
- 22. Measure the voltage at the engine coolant temperature sensor connector with the key on, engine off. It should be less than 5 volts. If it’s above 4.9 volts, continue.
- 33. With the engine running, use a scan tool to monitor the actual coolant temperature reading. Confirm it's within normal operating temperature range (195°F - 220°F). If the reading is wrong or shows a major discrepancy from a known good value, continue.
- 44. Disconnect the coolant temperature sensor and measure resistance across terminals. At room temp (around 70°F), you should see about 2.5k ohms. If it’s significantly off, replace the sensor.
- 55. Reconnect the sensor and retest the system. If the code returns, inspect the wiring for shorts to power or grounding issues.
Common causes
- Faulty engine coolant temperature sensor
- Shorted wiring or connectors
- Corroded connectors
- Faulty ECM (in rare cases)
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's drivable, but monitor your coolant temperature closely and fix it soon to avoid potential overheating.
Will the code come back after reset?
If the problem is not resolved, the code will likely return after a short drive.
Why do I see this paired with other codes?
Multiple codes can indicate a wider issue affecting the cooling system or faulty sensor data.
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