Engine Coolant Temperature
Indicates a fault in the engine coolant temperature sensor circuit.
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)
Your engine computer reads the coolant temperature to manage engine efficiency; if it sees something out of range, it triggers this code.
What the computer is actually seeing
The engine control module (ECM) monitors the voltage signal from the coolant temperature sensor, which should typically be between 0.5V (cold) and 4.5V (hot). If the voltage is out of range, the ECM records SPN 201.
What a healthy reading looks like
Coolant temperature should be around 195°F (90°C) to 220°F (104°C) when the engine is at normal operating temperature. Voltage from CTS should be approximately 0.5V at 32°F (0°C) and reach about 4.5V at 248°F (120°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 and condition—ensure it’s at the proper level and not contaminated. If coolant is low, top it off and see if the code returns. Decision: If the code persists, move to step 2.
- 22. Inspect the coolant temperature sensor wiring and connectors for any signs of damage, corrosion, or loose connections. Repair as necessary. Decision: If repairs are made, clear the code and test drive. If code returns, go to step 3.
- 33. Measure the voltage at the coolant temperature sensor connector with the engine running at operating temperature. Expected voltage should be within 0.5V to 4.5V. Decision: If voltage is out of range, replace the coolant temperature sensor. If within range, suspect ECM issue.
Common causes
- Faulty coolant temperature sensor
- Wiring issues or poor connections
- Short circuit to ground or power in the sensor circuit
- Faulty engine control module (ECM)
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's generally drivable, but monitor engine temperature closely; overheating can lead to serious damage.
Will this code come back after clearing?
If the underlying issue isn't resolved, it will likely return after a short period.
Why does this code sometimes pair with other codes?
Multiple codes can indicate issues in the engine cooling system, as sensor failures may affect overall performance.
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