P0115 moderate

Engine Coolant Temperature Sensor 1 Circuit

The P0115 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Temperature Sensor 1 Circuit. This is a moderate severity code.

My Garage →

Keep driving?: Yes, but fix soon
DIY difficulty: easy
Estimated cost: $15-$50 for ECT sensor

Recommended Tool

ANCEL AD310 OBD-II Scanner

Best-selling code reader on Amazon. Reads and clears check engine codes on any 1996+ vehicle. Under $30.

Check Price on Amazon

Affiliate link -- we earn a commission at no extra cost to you.

Every Tech Needs This

AstroAI Digital Multimeter

Essential for diagnosing sensor codes, checking voltage, and testing circuits. Under $15 and pays for itself on the first job.

Check Price on Amazon

Affiliate link -- we earn a commission at no extra cost to you.

Common Symptoms

Check Engine Light on
Temperature gauge erratic or pegged
Poor fuel economy
Rich running
Hard cold starts

Probable Causes (Ranked by Likelihood)

Faulty ECT sensor Very High
Wiring harness damage at sensor connector High
Corrosion at ECT sensor connector High
Open or short in ECT circuit wiring Moderate
PCM input circuit fault Low

Step-by-Step Diagnostic Procedure

With key on/engine cold, ECT sensor should read near ambient temperature. A reading of -40F or above 300F indicates a circuit fault.
Inspect the sensor connector for corrosion, bent pins, or green residue from coolant leaks.
Measure ECT sensor resistance cold (typically 2,000-3,000 ohms at 70F) and compare to spec chart.
Check wiring from sensor to PCM for opens or shorts.
Replace sensor and retest.

Common Fixes by Vehicle

What techs usually find when diagnosing P0115 on specific vehicles — tap your vehicle for the fix and the exact part:

2010-2020 Hyundai Sonata/Kia Optima 2.4L Easy DIY

Engine coolant temperature sensor circuit malfunction. The ECT sensor (Hyundai 25500-2GTA0) is located near the thermostat housing. Check the connector for coolant contamination from a leaking thermostat housing gasket. Test sensor resistance -- should be about 2.5K ohms at 68F and 300 ohms at 176F. Replace if out of spec.

Labor: 20-30 min

Common fix part Engine Coolant Temperature Sensor View on Amazon→ Compare fitment at PartsGeek→

2007-2017 Toyota Camry/Corolla 2.5L Easy DIY

ECT sensor signal is erratic or out of range. Located near the thermostat housing on the cylinder head. Check the connector for corrosion. Test resistance: approximately 2.5K ohms at 68F. If the gauge reads full cold or full hot with a warm engine, the sensor has failed. Replace with Denso 193-0002. Drain some coolant before removal to prevent air pockets.

Labor: 20-30 min

Common fix part Engine Coolant Temperature Sensor View on Amazon→ Compare fitment at PartsGeek→

2009-2019 Dodge Ram/Charger 5.7L Hemi Easy DIY

The ECT sensor on the Hemi is located on the front of the engine near the thermostat housing. Check for coolant leaks at the sensor O-ring that could contaminate the connector. If the scanner shows -40F with a warm engine, the circuit is open. Replace with Mopar 5149077AB. Bleed the cooling system after replacement to prevent air pockets.

Labor: 15-20 min

Common fix part Engine Coolant Temperature Sensor View on Amazon→ Compare fitment at PartsGeek→

Frequently Asked Questions

Can a bad ECT sensor cause overheating?

Not directly, but a faulty reading may prevent the radiator fan from engaging on time. Additionally, if the gauge reading is inaccurate, you may not notice genuine overheating until it is too late. Address ECT codes promptly.