P0115: Engine Coolant Temperature Circuit
Can you still drive? Yes, but the engine may not warm up properly or cooling fans may behave erratically. Avoid driving in extreme heat if the fans are not activating, as this can cause overheating.
What Does P0115 Mean?
Code P0115 indicates a general malfunction in the engine coolant temperature (ECT) sensor circuit. The ECT sensor is a thermistor that changes resistance with temperature, and the ECM uses this signal for fuel injection, ignition timing, cooling fan control, and transmission shifting. P0115 is set when the signal is erratic or does not follow expected warm-up patterns.
Need to read your codes?
An OBD-II scanner lets you read and clear diagnostic trouble codes from your vehicle's computer. Most scanners work with any car made after 1996.
Browse OBD-II Scanners on AmazonCommon Causes
- Faulty engine coolant temperature sensor
- Damaged wiring or connector to ECT sensor
- Low coolant level exposing the sensor
- Corrosion in ECT sensor connector
- Short or open in signal circuit
Symptoms
- Check engine light on
- Cooling fans may run constantly or not at all
- Poor fuel economy especially when cold
- Hard starting
- Incorrect temperature gauge reading
Diagnostic Steps
- 1Read ECT sensor value on scan tool with engine cold and compare to ambient temperature
- 2Monitor ECT reading during warm-up for smooth and steady increase
- 3Inspect ECT sensor connector and wiring for damage or corrosion
- 4Measure ECT sensor resistance and compare to specification chart
- 5Verify 5V reference and ground at sensor connector
- 6Test with a known good ECT sensor
Recommended Parts & Tools
engine coolant temperature sensor
electrical contact cleaner
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $25 - $200 |
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Frequently Asked Questions
What happens when the ECT sensor fails?
When the ECT sensor fails, the ECM cannot accurately determine engine temperature. This can cause hard starting, poor fuel economy, incorrect fan operation, and the engine may stay in open-loop fuel control longer than normal.
How do I test an ECT sensor?
Measure the sensor resistance with a multimeter when the engine is cold. A typical reading at 70 degrees F is about 2,000-3,000 ohms. At operating temperature (200 degrees F), it should drop to about 200-300 ohms. Compare to your vehicle-specific chart.
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