Engine Coolant Temperature Sensor 1
High engine coolant temperature detected.
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 engine computer thinks the coolant is hotter than 255°F (about 124°C).
What the computer is actually seeing
The Engine Control Module (ECM) monitors the coolant temperature sensor input, which should send a voltage signal between 0.5V (cold) and 4.5V (hot). A reading over 4.5V is considered a fault.
What a healthy reading looks like
Expected voltage from the coolant temperature sensor in normal operating conditions is around 2.5V at 190°F (88°C).
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 coolant level – should be at or above the minimum mark. If low, top it up and see if code returns.
- 22. Inspect the wiring and connector for the coolant temperature sensor – look for frays, breaks, or corrosion. Repair if necessary.
- 33. Measure the voltage at the coolant temperature sensor connector with the ignition on (engine off) – should be between 0.5V and 4.5V.
- 4 - If out of range, replace the coolant temperature sensor.
- 5 - If within range, proceed to check actual coolant temperature with a scanner.
Common causes
- Faulty coolant temperature sensor
- Wiring issues or short circuit
- Coolant level too low
- Thermostat stuck closed
Typical repair cost
$$ (100-300)
Related codes
Frequently asked questions
Is it safe to drive with this code?
It may drive okay, but expect overheating, which can cause severe engine damage.
Will this code come back after repair?
If the underlying issue is correctly identified and fixed, it should not return.
Why does it appear with SPN 1101?
SPN 1101 is often triggered alongside SPN 1102 due to related coolant temperature sensor issues.
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