What causes fault code P0115?

• Most likely: Faulty Engine Coolant Temperature (ECT) sensor (internal open or short) • Likely: Corrosion or damaged pins in the sensor connector • Possible: Wiring harness open circuit or short to ground between sensor and ECM • Rare: Thermostat stuck open (though usually triggers P0128) • Rare: Internal Engine Control Module (ECM) failure

Powertrain (Engine & Gearbox)Standard EOBD

P0115 - Engine Coolant Temperature (ECT) Sensor 1 Circuit Malfunction

Q: What are the symptoms of fault code P0115?

• Check Engine Light (MIL) illuminated • Hard starting (especially when cold) • Engine enters 'Limp Mode' (reduced power) • Cooling fans running continuously at high speed (failsafe mode) • Poor fuel economy and black smoke from exhaust • Erratic idling • Emissions test failure

Q: How do you fix fault code P0115?

STEP 1: Inspect the sensor connector for corrosion, moisture, or backed-out pins. Clean and secure as needed. STEP 2: Verify reference voltage. Disconnect the sensor and measure between the pins in the harness connector with ignition ON; it should read approximately 5.0V. STEP 3: Test sensor resistance (Ohms) using a multimeter. Typically, at 20°C (68°F), resistance should be approx. 2000-3000 Ohms; at 90°C (194°F), approx. 200-300 Ohms. STEP 4: Use a scan tool to monitor 'Live Data'. If coolant temp fluctuates wildly between -40°C and +140°C, a wiring or connector fault is indicated. STEP 5: If wiring and reference voltage are correct but sensor resistance is out of spec, replace the ECT sensor.

Last updated:1 February 2026

Related:ECT sensor, Engine Control Module (ECM/PCM), Thermostat, Kablage och kontaktstycken

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0100

Mass or Volume Air Flow A Circuit Malfunction

P0101

Mass or Volume Air Flow Circuit Range/Performance Problem

P0102

Mass Air Flow (MAF) Circuit Low Input

P0103

Mass or Volume Air Flow Circuit High Input

Technical Description

P0115 is set when the Engine Control Module (ECM/PCM) detects an implausible voltage signal from the Engine Coolant Temperature (ECT) sensor. The sensor is an NTC (Negative Temperature Coefficient) thermistor, where resistance decreases as temperature increases. The ECM applies a 5V reference; if the return voltage remains outside the calibrated range (typically below 0.1V or above 4.9V) for a specific duration, the code triggers. This fault disrupts closed-loop fuel control and ignition timing, as the ECM cannot accurately determine engine thermal state.

Possible Causes

Faulty Engine Coolant Temperature (ECT) sensor (internal open or short)

Corrosion or damaged pins in the sensor connector

Wiring harness open circuit or short to ground between sensor and ECM

Thermostat stuck open (though usually triggers P0128)

Internal Engine Control Module (ECM) failure

Symptoms

Check Engine Light (MIL) illuminated

Hard starting (especially when cold)

Engine enters 'Limp Mode' (reduced power)

Cooling fans running continuously at high speed (failsafe mode)

Poor fuel economy and black smoke from exhaust

Erratic idling

Emissions test failure

Do you also have
other fault codes?

See how P0115 connects with your other fault codes. Our advanced analysis tool identifies causal relationships and root causes directly.

Analyze multiple codes

P0115 - Engine Coolant Temperature (ECT) Sensor 1 Circuit Malfunction

Related Fault Codes

Technical Description

Possible Causes

Symptoms

Recommended Solution

Workflow

Mechanic's Tip

Do you also have
other fault codes?

P0115 - Engine Coolant Temperature (ECT) Sensor 1 Circuit Malfunction

Related Fault Codes

Technical Description

Possible Causes

Symptoms

Recommended Solution

Workflow

Mechanic's Tip

Do you also have other fault codes?

Do you also have
other fault codes?