Incorrect Engine Cooling System Temperature
The engine's cooling temperature is out of normal range.
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 coolant temperature sensor is reporting a reading that doesn't match the expected temperature. For example, it might say the coolant is -10°F when it should be around 180°F when warmed up.
What the computer is actually seeing
The engine control unit (ECU) receives a voltage signal from the coolant temperature sensor. A normal reading should be between 0.5V to 4.5V, corresponding to a temperature range of about 32°F to 250°F. If it's too low or too high, it triggers this fault code.
What a healthy reading looks like
Coolant temperature should be between 180°F and 220°F during normal operation; sensor voltage output should be between 0.5V and 4.5V.
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 and top off if low. Decision: Is the coolant level OK? If no, fill and retest.
- 2Inspect the wiring and connectors leading to the coolant temperature sensor for damage or corrosion. Decision: Are all connections secure and intact? If no, repair or replace the damaged wiring or connector and retest.
- 3Using a scan tool, monitor the coolant temperature reading while the engine is warming up. Decision: Does the reading reach 180°F to 220°F? If no, proceed to replace the coolant temperature sensor.
- 4Clear the fault codes and take the vehicle for a road test. Decision: Does the code reappear after the test? If yes, you may need to check the engine control unit or further diagnose the cooling system.
Common causes
- Faulty coolant temperature sensor
- Wiring issues or damaged connectors
- Low coolant level
- Thermostat stuck in open position
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate severity; drive with caution but get it fixed soon to avoid overheating issues.
Will this code come back?
If the underlying issue isn't resolved, yes, it likely will.
Why does this code show up with SPN 1408?
SPN 1408 typically relates to a threshold breach on the temperature sensor, often indicating similar sensor or cooling system problems.
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