P0115: Engine Coolant Temperature Circuit Malfunction
Updated November 14, 2026
The coolant temperature sensor tells the engine computer how warm the engine is, which it uses for fuel mixture, idle speed and cooling fan control. P0115 means the computer has found a general electrical problem in that sensor's circuit, so it can't trust the reading and uses a backup value instead.
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🔧 Want to check this yourself? An OBD2 scanner reads the code; models with live data also show the sensor readings used in the checks below. See code readers and scanners from $24.99 ↓ · Which scanner do I need?
Common causes
- A failed engine coolant temperature sensor
- Damaged wiring or a loose or corroded connector at the sensor
- A problem with the sensor's 5-volt reference or ground circuit
- An engine computer fault (less common)
Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.
Symptoms
- Check engine light
- Cooling fans running all the time on many vehicles
- Hard starting, rough idle or poor fuel economy
- A temperature gauge that reads wrong, if it uses the same sensor
Is it safe to drive?
Watch the temperature gauge closely. If it reads hot, you see steam, or the engine is overheating, pull over safely, shut it off and have it towed. If the engine runs normally and the fans are working, it's usually OK to drive a short distance to get it fixed, but the computer can't protect the engine as well without a good temperature reading.
How to check it with a scanner
- Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
- Check the coolant level only when the engine is cold; never open a hot radiator cap or reservoir.
- Scan for related codes such as P0117, P0118 or sensor reference voltage codes.
- After the car has sat overnight, compare the coolant temperature and intake air temperature in live data before starting; they should be close.
- With the key off, inspect the sensor connector and wiring for corrosion, damage or a loose fit.
- After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.
A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.
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Some vehicles have one sensor for the engine computer and a separate one for the dash gauge; make sure you replace the one that sets the code.
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Questions
What does P0115 mean?
P0115 is the generic OBD2 code for "Engine Coolant Temperature Circuit Malfunction." The coolant temperature sensor tells the engine computer how warm the engine is, which it uses for fuel mixture, idle speed and cooling fan control. P0115 means the computer has found a general electrical problem in that sensor's circuit, so it can't trust the reading and uses a backup value instead.
Is it safe to drive with P0115?
Watch the temperature gauge closely. If it reads hot, you see steam, or the engine is overheating, pull over safely, shut it off and have it towed. If the engine runs normally and the fans are working, it's usually OK to drive a short distance to get it fixed, but the computer can't protect the engine as well without a good temperature reading.
How do I check P0115 myself?
Read the code and freeze-frame data with an OBD2 scanner, then: Check the coolant level only when the engine is cold; never open a hot radiator cap or reservoir. Scan for related codes such as P0117, P0118 or sensor reference voltage codes. After the car has sat overnight, compare the coolant temperature and intake air temperature in live data before starting; they should be close. With the key off, inspect the sensor connector and wiring for corrosion, damage or a loose fit.
Related codes
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