Engine Coolant Temperature Circuit High Input
The engine computer detected a high signal from the coolant temperature sensor.
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What it means (plain English)
The coolant temperature sensor is reporting a temperature that is too high, usually around 5V on the signal line when it shouldn't be, meaning the ECU thinks the engine is overheating even if it isn't.
What the computer is actually seeing
The engine control module (ECM) is monitoring the coolant temperature via the sensor. When the signal voltage exceeds the normal operating range (typically around 0.5V to 4.5V), it throws this code.
What a healthy reading looks like
Normal operating voltage for the sensor should be between 0.5V to 4.5V corresponding to 0°C to 100°C (32°F to 212°F).
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 coolant level and top off if low (normal range should be between min and max marks).
- 2Inspect the wiring and connectors for damage or corrosion at the coolant temperature sensor—ensure they are securely connected (look for frayed wires, corrosion).
- 3Back-probe the coolant temperature sensor connector, observing voltage while the engine is running—should be within 0.5V to 4.5V. If over 4.5V, proceed to the next step. If within range, consider replacing the sensor.
- 4Disconnect the coolant temperature sensor and measure resistance with a multimeter while cooling the engine down. It should read approximately 2.5k ohms at 25°C (77°F). If it reads near 0 ohms, the sensor is likely faulty.
- 5If wiring, connectors, and the sensor all pass but the code persists, inspect the ECM for possible internal faults.
Common causes
- Shorted wiring to the sensor
- Faulty coolant temperature sensor
- Poor electrical connections at the sensor
- Faulty engine control module (ECM)
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with a P0118 code?
It's moderately serious; you can drive to the shop, but be cautious of overheating.
Will this code come back after clearing it?
It may come back if there's a persistent issue, such as faulty wiring or a bad sensor.
Does this issue pair with other codes?
Yes, it is often seen alongside codes indicating coolant sensor issues like P0117 (low input) or others affecting engine temperature.
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