P0115: Engine Coolant Temperature Sensor 1 Circuit
What to do
Have it checked promptly. The cooling fans may not run when they should, which risks overheating in traffic even though the engine itself is healthy.
What this code means
A circuit fault in the engine coolant temperature sensor. This reading drives more decisions than almost any other: cold-start enrichment, when closed-loop fuelling begins, cooling fan operation, and on many vehicles the temperature gauge itself. Note that vehicles often carry two coolant sensors — one for the control module and one for the gauge — so a working gauge does not rule this code out.
Likely causes
Start here
- Faulty engine coolant temperature sensor · easy
- Corroded or loose connector · easy
- Open circuit in sensor wiring · moderate
Less common
- Low coolant level · easy
Rare
- Failed control module · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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