Invalid Engine Coolant Temperature Signal
The engine control unit has received an erroneous signal for coolant temperature.
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What it means (plain English)
The engine computer is getting a temperature reading from the coolant sensor that doesn't make sense, like it's too low or too high too fast.
What the computer is actually seeing
The engine coolant temperature (ECT) sensor is supposed to send a voltage signal representing the coolant temperature. If the temperature is 90°C, the voltage should be around 0.5V. If the signal is intermittent or a sensor failure occurs, the ECT may read a constant 5V signal or fluctuate wildly, triggering this fault code.
What a healthy reading looks like
Normal ECT range is between 85°C and 110°C, which corresponds to a sensor voltage of approximately 0.4V to 2.5V.
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.
- 11. Check the engine coolant level; ensure it's within the proper range. Decision: If low, refill and retest. If not low, proceed to the next step.
- 22. Inspect the wiring and connector at the ECT sensor for damage or corrosion. Decision: If damaged, repair or replace as necessary. If no damage, proceed to the next step.
- 33. Measure the voltage at the ECT sensor with the engine at operating temperature. Expected: ~0.4V to 2.5V. Decision: If outside this range, replace the ECT sensor. If within this range, proceed to next step.
- 44. Check the ECM for fault codes and inspect related circuits. Decision: If ECM shows other codes or faults, repair those before re-testing this code.
Common causes
- Faulty engine coolant temperature sensor
- Wiring issues (shorts or opens) in the coolant temperature circuit
- Faulty engine control module (ECM)
- Coolant leaks affecting sensor operation
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's generally safe but you should fix it soon as it can impact fuel efficiency and engine performance.
Will this code come back after clearing it?
If the underlying issue isn't resolved, yes, it will likely return.
Why does this code appear with other related codes?
Many times, issues like faulty sensors or wiring can cause multiple miscommunication errors between the engine and the ECM.
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