Coolant Temperature Sensor 1 - Voltage Too High
The coolant temperature sensor is sending a high voltage signal to the engine control unit.
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What it means (plain English)
The coolant temperature sensor measures the engine's temperature, and if it sends a voltage above about 4.9 volts, the computer thinks something's wrong.
What the computer is actually seeing
The Engine Control Module (ECM) expects the coolant temperature sensor output to be between 0.5 to 4.5 volts when measuring normal operating temperatures. A reading above 4.9 volts indicates a fault.
What a healthy reading looks like
0.5 to 4.5 volts (normal operation); above 4.9 volts (fault)
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.
- 1Check the engine coolant level; ensure it's not low or empty.
- 2Inspect wiring and connector for damage; look for frays, breaks, or corrosion.
- 3Disconnect the coolant temperature sensor connector, measure resistance across terminals. Should be near 0 ohms if good, check against manufacturer specs for expected values.
- 4Reconnect the sensor and measure the voltage at the connector with the engine running; voltage should be between 0.5 - 4.5 volts. If above 4.9 volts, replace the sensor.
- 5If sensor is within expected values, check ECM for faults and perform further diagnostics.
Common causes
- Shorted coolant temperature sensor
- Open or shorted wiring harness
- Faulty engine coolant temperature sensor
- Corrosion in the connector pins
- Poor ground connection to the sensor
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It can be drivable, but monitor engine performance closely and check for overheating.
Will this problem come back after clearing the code?
If the underlying issue isn't fixed, it likely will return.
Why does this code often come with other codes?
Multiple codes often indicate related problems, particularly with sensors that monitor similar systems.
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