P0115: Engine Coolant Temperature Sensor 1 Circuit – Meaning, Symptoms, Causes, and How To Fix It

The P0115 trouble code stands for Engine Coolant Temperature Sensors 1 Circuit which means the vehicle’s computer has detected bad input signals coming from the engine coolant temperature (ECT) sensor circuit. The engine coolant temperature sensor informs the vehicle’s computer about the current temperature of the engine so that the fuel injection and ignition timing can be properly adjusted. If the ECT sensor isn’t able to send out information due to a bad circuit, a P0115 trouble code will be triggered.

Key Takeaway

  • The P0115 trouble code stands for Engine Coolant Temperature Sensor 1 Circuit.
  • It can affect almost all vehicles on the market.
  • The P0115 trouble code can be caused by a bad ECT sensor, damaged ECT sensor connector, shorted ECT sensor signal circuit, overheated engine, low coolant level, or air in the cooling system.
  • The most common symptoms of a P0115 code include check engine light, hard starting, decreased fuel economy, engine running rich, engine running lean, engine stalling, and engine overheating.
  • It’s not safe to drive with a P0115 code because the engine can overheat without any warning.
  • To diagnose a P0115 code, you need to scan your vehicle with an OBD2 scanner, and verify that power is getting to the ECT sensor with the help of a multimeter.
  • Repairing the P0115 code costs between $80 – $150 depending on make and model.

What Does The P0115 Code Mean?

P0115 Engine Coolant Temperature Sensor 1 Circuit – Meaning, Symptoms, Causes, and How To Fix It

The P00115 is a diagnostic trouble code that suggests the Engine Coolant Temperature Sensor 1 Circuit has malfunctioned. The engine coolant temperature (ECT) sensor has the purpose of measuring the temperature of the engine and sending it to the vehicle’s computer. When the engine coolant temperature sensor is unable to perform its task due to a faulty circuit, a P0115 code will be triggered.

A coolant temperature sensor works by measuring the temperature of the engine’s coolant. The sensor detects changes in the coolant temperature and relays this information to the engine control unit. This helps to regulate things like fuel injection levels and ignition timing to help ensure your engine runs efficiently.

How a Coolant Temperature Sensor Works

The engine coolant temperature sensor found in most vehicles is electrically operated. Since this sensor is electrically operated, its readings are highly accurate and reliable compared to manual measurements. However, when the power supply to the engine coolant temperature sensor fails, a P0115 code will be triggered.

The accuracy of the readings from a coolant temperature sensor is very important for proper engine operation, as operating either too hot or too cold can be damaging to engine components or result in poor performance.

Which Vehicles Are Affected By The P0115 Code

MakeAffected By P0115 Code
ToyotaYes
NissanYes
ChevroletYes
BMWYes
AudiYes
BuickYes
MercedesYes
GMCYes
SuzukiYes
TataYes
LexusYes
MazdaYes
MitsubishiYes
KiaYes
JeepYes
FiatYes
HondaYes
HyundaiYes
OpelYes
FordYes
FiatYes
PeugeotYes

What Are The Possible Causes of The P0115 Code?

The most common causes of a P0115 code include a bad engine coolant temperature (ECT) sensor, damaged connector, shorted circuit, overheated engine, low coolant level, or air in the cooling system. All of these can contribute to the premature wear of the ECT sensor and the P0115 code.

1. Bad ECT sensor

The engine coolant temperature sensor in cars is an essential component used to measure the temperature of the car’s coolant system. This data allows the electronic control unit (ECU) to regulate and adjust various parameters, including fueling, timing, and idle speed. It also helps alert drivers via warning lights when the engine is potentially overheating or operating at a higher-than-normal temperature.

Without a functioning temperature sensor, it would be difficult for the ECU to accurately manage a car’s performance and fuel efficiency, while also ensuring safe engine temperatures are maintained. As a result, the P0115 trouble code will be triggered.

2. Damaged ECT sensor connector

The engine coolant temperature sensor in cars plays an important role in the performance of a vehicle. The connector – which is often made of plastic or metal, depending on the type of car – allows for electrical current to pass through the sensor, connecting it to the car’s computer system. This connection provides information about the engine coolant temperature so that the computer can make necessary adjustments and keep the car running smoothly and safely.

If the ECT sensor connector is damaged, the ECT sensor will not be able to operate properly and a P0115 code will be triggered.

Operating a car or other motor vehicle without a functioning engine coolant temperature sensor connector can be an extremely dangerous proposition. Coolant temperature is essential for ensuring that your vehicle’s engine does not overheat and cause lasting damage, so any issues with the connector should be addressed quickly and efficiently in order to keep your motor running properly.

Physically inspecting the damaged piece and replacing it accordingly is usually the best course of action in repairing the damaged connector, as attempting to repair it with makeshift materials can result in reduced performance of your engine or even further damage down the line.

3. Shorted ECT sensor signal circuit

A shorted ECT sensor signal circuit occurs when power from the battery is sent down a different route than was originally intended, creating an electrical overload that has the potential to cause significant damage.

It can occur for a number of reasons, most commonly due to frayed or damaged wiring, it can also be caused by something like corroded battery terminals or faulty spark plugs. When this happens, the ECT sensor fails to report the temperature of the engine properly and a P0115 code will be triggered.

Faulty engine coolant temperature sensors can cause a range of issues with your vehicle, from excessive fuel consumption to overheating.

4. Engine overheating

Engine overheating can be detrimental to a car, but it can also irreversibly damage the engine coolant temperature sensor. If an engine is routinely subjected to higher temperatures, the coolant temperature sensor weakens from the exposure and can fail.

The normal operating temperature range for most engine coolant temperature sensors is from 32 degrees Fahrenheit to 221 degrees Fahrenheit. Anything above 221 degrees Fahrenheit can cause the engine coolant temperature sensor to fail and trigger a P0115 code.

5. Low coolant level

Driving a vehicle with a low coolant level will cause the engine to eventually overheat. The temperature that an overheated engine release is enough to damage the engine coolant temperature sensor. When the ECT sensor is damaged, a P0115 code will be triggered.

If a car has low coolant levels, it can lead to major engine damage and even complete failure. Coolant is essentially the lifeblood of your car engine, allowing it to run smoothly and reliably by regulating temperatures. Properly maintained coolant levels are key to ensuring that your engine continues to function well over its lifetime.

6. Air in the cooling system

Having air in the cooling system is equivalent to not having coolant. The air pocket can prevent coolant from moving freely throughout the engine block and radiator, resulting in overheating. When the engine overheats, it reaches a temperature of 220 degrees Fahrenheit which is the limit of the engine coolant temperature sensor. This will cause the ECT sensor to fail and trigger a P0155 code.

What Are The Common Symptoms of The P0115 Code?

The most common symptoms of the P0115 code include illuminated check engine light, hard starting when the engine is cold, decreased fuel economy, engine running rich or lean, engine stalling until it is warmed up, and engine overheating.

1. Check engine light

One of the major symptoms of a failed engine coolant temperature sensor (P0115) is when the check engine light turns on. This is caused by the sensor’s inability to provide the vehicle’s computer with accurate information regarding the current engine coolant temperature.

The car’s computer needs this information so that it can adjust parameters such as fuel injection and ignition timing to ensure that your car engine runs efficiently, without overworking itself or breaking down. When the sensor fails, it sends inaccurate information, confusing your car’s computer and causing it to alert you through the check engine light.

Diagnosing and replacing a failed engine coolant temperature sensor as soon as possible can help minimize potential damage to your car’s engine and save you costly repair bills in the future.

2. Hard starting

Hard starting is a common symptom of a faulty engine coolant temperature sensor (P0115), and it can cause no small amount of worry for car owners. A failed engine coolant temperature sensor, or ECTS, can prevent ignition timing from being properly adjusted based on engine temperature.

This essential component helps ensure efficient fuel combustion, which helps the engine get off the mark quickly and smoothly. Without the precise control achieved by a functioning ECTS, hard starting is sure to occur when an engine is cold or hot.

Avoiding hard starting due to a failed ECTS means having your vehicle inspected if you experience symptoms such as excessive sputtering or stalling when trying to start your car.

3. Decreased fuel economy

The engine coolant temperature sensor is an important component of a car’s internal combustion system. When the engine coolant temperature sensor fails (P0115), it can have serious consequences for fuel consumption – and ultimately your wallet!

In essence, a failed engine coolant temperature sensor reduces the efficiency of the engine by not accurately monitoring temperatures during operation. The resulting fluctuating temperatures increase pressure on other engine components and reduce overall fuel efficiency; so not only are you now using more fuel, but you’re also putting stress on other parts which can lead to more costly damage down the road.

4. Engine running rich

What Are The Common Symptoms of The P0115 Code

If a vehicle’s engine coolant temperature sensor is malfunctioning (P0115), one of the associated symptoms is that the engine may run rich. This means that too much gasoline is being directed into the combustion chamber, and not enough air is present to help create a perfect air/fuel ratio balance.

When this happens, the engine may run rough or stall entirely – because too much fuel is not combusting with the amount of air that’s available. In some cases, an overly rich mixture will cause excess smoke from the tailpipe and can reduce fuel economy significantly as well.

To diagnose this issue and determine if it is linked to a failed engine coolant temperature sensor, it’s best to bring your car in for a diagnostic check-up from a specialist.

5. Engine running lean

The engine coolant temperature sensor is an important component of a car’s operation since it helps to regulate the engine’s temperature. If the sensor fails (P0115), it can have serious consequences for your vehicle. One symptom of a failed engine coolant temperature sensor is the engine running lean, which occurs when there is too much air and not enough fuel in the combustion chamber.

This happens because a malfunctioning coolant temperature sensor causes incorrect air-fuel ratios in the mixture, creating an imbalance that usually leads to insufficient amounts of fuel being delivered to the cylinders.

Without proper levels of fuel, the engine runs at an efficient level but without enough power output or acceleration capacity. It’s important that you take note of any symptoms such as an engine running lean to avoid further damage or deterioration of your car’s functions down the line.

6. Engine stalling

What Are The Common Symptoms of The P0115 Code

When a vehicle’s engine coolant temperature sensor fails (P0115), the vehicle’s engine can begin stalling. This is because the failed temperature sensor cannot properly send information to the vehicle’s computer.

Without this knowledge concerning the actual temperature of the engine’s coolant, the computer cannot determine precisely how much fuel to inject into the engine. As a result, an excessively large or small amount of gasoline may be sent to the engine at any given time, resulting in frequent stalling and other issues with the running and performance of the vehicle.

7. Engine overheating

When an engine coolant temperature sensor fails (P0115), the most immediately noticeable symptom is engine overheating. This is because the primary purpose of the sensor is to measure and track the temperature of the coolant as it circulates around the engine.

If it does not function properly, then the car’s computer cannot accurately determine how hot or cold the coolant is and may misinterpret this data, causing it to incorrectly adjust operations like fan speeds and fuel-air mixture in response.

As these essential components are not operating within their expected parameters, a higher rate of heat buildup typically results, leading to engine overheating.

Is It Safe To Drive With a P0115 Code

It is not safe to drive with a P0115 code (Engine coolant temperature sensor malfunction) because this sensor is a critical component that affects the cooling and fueling of the engine by providing readings of the engine temperature. If you drive with a P0115 code, the engine can overheat without any warnings.

The engine coolant temperature sensor is an essential component of any vehicle, enabling the car to adjust its engine revolutions and fuel-air mixture in order to ensure that it runs optimally. The coolant temperature sensor does this by monitoring the temperature of the engine’s coolant, alerting the car when a certain temperature threshold has been reached.

By keeping engine temperatures within an optimal range, particularly when a high load is placed on the engine, this sensor plays an important role in ensuring safe and reliable operation while also increasing performance efficiency.

When the engine coolant temperature sensor fails, there can be serious consequences. Without this critical component in peak working condition, it can allow the engine to overheat due to a lack of temperature information – which can then cause long-term damage further down the line. Such damage could require expensive repairs or worse still, result in an unsafe driving experience for the driver and their passengers.

It’s therefore essential that drivers pay close attention to their vehicles and are aware of any potential signs of deterioration from the engine coolant temperature sensor so that any potential risks are avoided before they become an issue.

How To Diagnose The P0115 Code (Engine Coolant Temperature Sensor)

Diagnosing a P0115 code requires a complete vehicle scan that will show any trouble codes that the vehicle has and actually inspecting the broken part which in this case is the engine coolant temperature sensor.

1. Scan the vehicle with an OBD scanner

P0115 Code

In order to diagnose a P0115 code, you will need to hook up an OBD2 scanner to the vehicle’s computer port. This is usually located underneath the steering wheel, but it can also be found in the engine bay. Hook up the OBD2 scanner and scan the vehicle for trouble codes. When done, you should have a P0115 Engine coolant temperature sensor 1 circuit code.

2. Locate the engine coolant temperature sensor

P0115 Code

Locating the engine coolant temperature sensor can be easy or difficult depending on your make and model of car. In vehicles manufactured before 2000, the engine coolant temperature sensor is typically located near the top of the engine in a circular plug-in assembly. Modern cars require further disassembly to reach the sensor, often beginning with the removal of air ducts, intake manifold covers, or hoses.

What I like to do before trying to locate the engine coolant temperature sensor is to perform a Google search and see how the ECT sensor looks for the vehicle that I am working on. The ECT sensor is most likely to be near the engine and will have an electrical connector on top.

3. Verify that power is getting to the sensor

In some cases, power is not getting to the sensor. This will trigger the P0115 code even though the ECT sensor is working. So, disconnect the power harness and test to see if power is getting to the sensor. For this, you will need a voltmeter. Turn the ignition key to the on position and place the black lead on a metal part of the engine(ground) and the red lead directly into the power harness.

You should get around five volts. If the voltage readings are very low like one or two volts, it is a definitely concern. You should proceed to find any damages on the wiring. However, if you tested that enough power is getting to the engine coolant temperature sensor, continue to the next step.

4. Remove the ECT sensor and test it

P0115 Code

The ECT sensor is held in place by a 19-millimeter bolt, Using a wrench, remove the ECT sensor to test it further. On the top of the ECT sensor, you will notice two metal prongs. Through these prongs, the ECT sensor gets the electrical power and sends out the readings. Grab a multimeter and set it on OHMs. Touch the red lead to one prong and the black to the other prong. You should get a reading between 1.5 and 2 Ohms. If you are getting low readings or no readings at all, it means that the engine coolant temperature sensor is faulty.

How Much Does It Cost To Repair P0115 Code

MakeP0115 Part CostP0115 Labor CostP0115 Total Repair Cost
Toyota$34.38$80$114.38
Nissan$19.92$80$99.92
Chevrolet$15.53$80$95.53
BMW$20.07$80$100.07
Audi$15.17$80$95.17
Buick$16.59$80$96.59
Mercedes$12.05$80$92.05
GMC$16.59$80$96.59
Suzuki$14.59$80$94.59
Tata$15.53$80$95.53
Lexus$34.38$80$114.38
Mazda$37.91$80$117.91
Mitsubishi$14.59$80$94.59
Kia$19.74$80$99.74
Jeep$22.68$80$102.68
Fiat$22.15$80$102.15
Honda$66.85$80$146.85
Hyundai$19.74$80$99.74
Opel$14.56$80$94.56
Ford$13.16$80$93.16
Fiat$15.01$80$95.01
Peugeot$14.56$80$94.56

What Repairs Can Fix The P0115 Code

Repairs that can fix the P0115 code include:

  • Replacing the bad engine coolant sensor with a new one which costs around $100 (depending on make and model).
  • Replacing the electrical connector that feeds power to the ECT sensor which costs about $30.
  • Replace any damaged wiring that runs from the ECT to the battery which can cost between $50 and $100 depending on how many wires are damaged.

How To Fix The P0115 Code (Engine Coolant Temperature Sensor)

The P0115 code is a diagnostics code that means the vehicle’s computer has detected bad readings coming from the engine coolant temperature sensor. Two things can contribute to the P0115 code: bad ECT sensor, or bad wiring/connectors. In order to fix the P0115, you must first determine what is the problem and then continue to fix it.

1. Scan the vehicle for trouble codes

P0115 Code

Connect the OBD2 scanner to the vehicle’s diagnostics port and run a scan. Make sure that you get a P0115 code before continuing any further.

2. Locate the ECT sensor

P0115 Code

The engine coolant temperature sensor is usually attached to the engine itself. Although the location of the ECT sensor may vary depending on the make and model, you can always refer to the owner’s manual for this information.

3. Visually inspect the electrical connector

P0115 Code

If the electrical connector is the reason for the P0115 code, you will know only by visually inspecting it. I am talking about a broken connector, damaged wiring, melted ports, etc. If this is the case, you can go ahead and replace the electrical wiring going to the ECT sensor. However, if everything looks normal without any visible damage, the fault might be lying in the ECT sensor itself.

4. Test the ECT sensor

To test the ECT sensor, you can use a multimeter and get an OHM reading from the sensor while the sensor is attached to the vehicle, or you can remove the sensor and place it in a hot water and then get a reading. I prefer the first one because it is more accurate. With the ignition turned to the on position, place the black lead as the ground and the red lead into the ECT sensor pin. You should get a reading of about 1.5 – 2.0 OHMs.

5. Replace the ECT sensor

P0115 Code

If you get low or no reading from the ECT sensor, you will need to replace it. Grab a 19-millimeter socket and remove the sensor. The bolt that holds the sensor in place is actually attached to the sensor itself. Then, go ahead and install the new ECT sensor and tighten it properly. Reattach the electrical connector and scan your vehicle for trouble codes. There should be no P0115 on the OBD2 scanner at this point.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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