Nissan Altima Replace Engine Coolant Temperature (ECT) Sensor To Fix DTC P0125

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Purpose

The article outlines the procedures to diagnose and confirm Diagnostic Trouble Code (DTC) P0125 on a 2019 Nissan Altima equipped with a 2.5L L4 engine and to replace the Engine Coolant Temperature (ECT) Sensor to resolve the issue.

Introduction

In cases where the Malfunction Indicator Lamp (MIL) on your vehicle’s dashboard is illuminated, and the Engine Control Module (ECM) has stored DTC P0125 (Insufficient Coolant Temp for Closed Loop Fuel Control), it indicates the ECM has detected that the engine coolant is not reaching the required temperature level in a specified amount of time to enable closed-loop fuel control. In a closed-loop fuel control system, the engine's air-fuel mixture is adjusted based on the data from various sensors, including the ECT sensor. A DTC may be set if the coolant temperature is too low or takes too long to reach the desired level. While drivability issues may not be present, this condition can still impact the engine's performance and emissions.

Symptoms of DTC P0125 include:

• Malfunction Indicator Lamp (MIL) is ON or flashing.
• Engine overheating.
• Constant high engine temperature.
• Rough idling or stalling.
• Poor fuel efficiency.

Possible causes of this fault are:

• Low engine coolant level.
• Faulty Engine Coolant Temperature (ECT) sensor.
• Faulty thermostat.

To learn more about the purpose and function of the ECT sensor, refer to Smart Diagnostic Training_Engine Coolant Temperature (ECT) .

When DTC P0125 is present on a 2014-2019 Nissan Altima, replacing the Engine Coolant Temperature sensor may resolve the issue.

(This image is for illustrative purposes only and may not match the actual part number)

Diagnostic Procedures:

Initial Inspection

During initial inspection, check for obvious signs of mechanical damage such as torn inlet boots, missing/broken vacuum hoses, and loose or disconnected wire harnesses. Always inspect the radiator and hose condition, check the coolant level and pressure check the system and cap for leaks before attempting to diagnose cooling system related faults. Refer to the vehicle emission warranty manual for time and mileage coverage for this and other emission related fault(s). For additional information, refer to the service manual or applicable TSB.

Diagnostic Procedures

Check the ECT Sensor:

a. Using a scan tool, access the Live Data (LD) function and monitor the ECT and Intake Air Temperature (IAT) value after an 8-hour soak. The value of the ECT should equal the value of the IAT sensor.

- If the scan tool values match each other and ambient temperature, check for intermittent loose and go to Step 1d.

- If the IAT and ECT do not match each other, and /or ambient temperature, go to Step 1b.

b. Disconnect the ECT sensor. Using a Digital Multimeter (DMM) with the ignition in the Key ON Engine OFF (KOEO) position, measure the voltage at two pins of the ECT sensor. Voltage should be 4.9–5.1V.

- If the voltage is out of specification, repair the wiring between the Powertrain Control Module (PCM) and ECT sensor. Perform Repair Validation.

- If the voltage is within specification, go to Step 1c.

c. Turn the ignition to the OFF position. Use a DMM to measure the voltage or resistance at the ECT sensor.

Specifications:

At -10°C, the voltage should be 4.4 Volts, the resistance should be 7000 – 11400 Ohms

At 20°C, the voltage should be 3.5 Volts, the resistance should be 2370 – 2630 Ohms

At 50°C, the voltage should be 2.2 Volts, the resistance should be 680 – 1000 Ohms

At 90°C, the voltage should be 1.0 Volts, the resistance should be 236 – 260 Ohms

- If voltage or resistance is within specification, go to Step 1d.

- If voltage or resistance is out of specification, replace the ECT sensor. Perform Repair Validation.

d. No fault is present. Operate the vehicle within the Freeze Frame (FF) parameters. If the Diagnostic Trouble Codes (DTC) sets, go to Step a.

Replace the ECT Sensor

The following procedure outlines the steps necessary to replace the ECT sensor. Keep in mind that the specific procedures will differ between vehicle makes and models., Always refer to your vehicle's service/repair manual or seek professional assistance if you require further clarification.

Important: Before starting any work on your vehicle:

Ensure the engine is cool to avoid burns or injuries

Disconnect the battery to prevent electrical hazards.

Tools and materials:

• 14mm wrench
• Phillips Screwdriver
• Drain pan
• Funnel
• New Engine Coolant Temperature Sensor

Removal

1. Locate the ECT sensor: The Engine Coolant Temperature (ECT) sensor is usually located on or near the engine's thermostat housing. On the 2019 Nissan Altima, the ECT is on the right side of the engine.

2. Drain the coolant (optional): In some cases, it may be necessary to drain a small amount of coolant to properly access and remove the sensor. To accomplish this, place a drain pan under the radiator drain plug. Open the drain plug and allow the coolant drain into the pan. Make sure to dispose of the coolant in a safe and appropriate manner.

3. Remove the electrical connector: Press the connector's locking tab (if equipped) and gently pull the connector away from the sensor. DO NOT pull on the wires directly, as this may damage the connector and/or wiring.

4. Remove the old sensor: Use a wrench to carefully unscrew the sensor. Turn the sensor counterclockwise to loosen and remove.

Installation

1. Install the new ECT sensor: Install the sensor and tighten by hand, making sure the threads are properly engaged. Use a wrench to tighten the sensor firmly. DO NOT overtighten, as this may damage the threads or the sensor.

2. Reconnect the electrical connector: Press the electrical connector firmly onto the new ECT sensor until you hear an audible click. This will ensure a proper connection. BE SURE the connector is securely attached.

3. Refill the coolant (if drained): If it was necessary to drain an amount of coolant during sensor removal, refill the coolant to the proper level. BE SURE to follow the manufacturer’s recommendations for coolant type and specifications. Use a funnel to pour coolant into the radiator or reservoir, as appropriate. following the manufacturer's recommended type and specifications. BE SURE to bleed air out of the coolant system when replacing fluid.

4. Check for leaks: Reconnect the battery. Start the engine and let it idle for a several minutes while observing the area around the new sensor for any coolant leaks.

Repair Validation:

1. Clear DTC and FF information.

2. Perform the KOEO and Key ON Engine RUNNING (KOER) tests or follow the On-Board Diagnostic (OBD2) drive cycle requirements for the fault area.

3. Optionally, operate the vehicle within the conditions recorded in the FF data.

4. Check for pending or stored DTCs. If none are found, the repair is complete.

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