Engine Coolant Temperature Sensor - Circuit Low
The ECM has detected a low voltage reading from the engine coolant temperature (ECT) sensor.
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What it means (plain English)
The engine coolant temperature sensor tells the computer how hot the engine is running. If the sensor sends a signal that's too low, it thinks the engine is too cold, which can mess with fuel delivery and emissions.
What the computer is actually seeing
The Engine Control Module (ECM) receives a voltage signal from the ECT sensor, typically ranging from 0.5V (cold) to 4.5V (hot). If it's seeing voltages below 0.5V, it triggers this fault code.
What a healthy reading looks like
Expect ECT sensor output between 0.5V and 4.5V, corresponding to temperatures from approximately -40°C to 125°C (-40°F to 257°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.
- 11. Check engine coolant level and top off if low. Decision: If low, refill and retest; if normal, proceed to step 2.
- 22. Inspect the ECT sensor wiring and connector for corrosion or damage. Decision: If damaged, repair/replace; if okay, proceed to step 3.
- 33. Measure the voltage at the ECT sensor connector with the ignition on (engine off). Decision: If below 0.5V, sensor or wiring issue likely; if above, proceed to step 4.
- 44. Replace the engine coolant temperature sensor and clear the code. Decision: If code returns, suspect ECM.
Common causes
- Faulty engine coolant temperature sensor
- Wiring issues or bad connectors in the ECT circuit
- Faulty Engine Control Module (ECM)
- Coolant level too low affecting sensor operation
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Yes, but drive cautiously and check for any overheating issues.
Will the code come back?
It might if the underlying issue isn't fixed or if the new part fails.
Why does this code pair with SPN 2198?
SPN 2198 is related to the same ECT sensor circuit but indicates a high voltage fault.
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