OBD-II Trouble Codes

P0115 Code: Engine Coolant Temperature Sensor 1 Circuit

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A vehicle’s engine accumulates heat as it operates. Engine coolant is a substance that’s circulated around the engine to absorb heat from the engine. With the help of the radiator and the rest of the engine cooling system, that heat is dispersed into the atmosphere. The primary function of the cooling system is to maintain the engine’s optimal operating temperature. Without this system, there is a high risk of overheating and engine damage.

The P0115 code indicates that there is a potential issue with the sensor that monitors the engine coolant temperature. Find out more about this trouble code with this informative guide.

image of a coolant temperature sensor
Code P0015 may be set when the PCM detects erratic or irrational input signals coming from the ECT sensor circuit.

What Does the P0115 Code Mean?

Diagnostic trouble code (DTC) P0115 stands for “Engine Coolant Temperature Sensor Circuit.” This code sets when the powertrain control module (PCM) detects erratic or irrational input signals coming from the engine coolant temperature (ECT) sensor circuit. The code may also register if the PCM detects an abnormally low or high voltage signal from the engine coolant temperature sensor circuit. The ‘1’ portion of the code points to sensor # 1 in vehicles with two coolant temperature sensors.

Note: The definition of code P0115 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

The engine coolant temperature sensor measures the temperature of the engine coolant. This two-wire sensor is a thermistor that changes resistance with temperature. One wire carries the 5V reference signal from the PCM and the other is the ground wire.

As the temperature of the engine coolant changes, the sensor’s resistance changes on its ground signal to the PCM. If the engine is cold, the sensor’s resistance is high, but if the engine is warm, the resistance is low.

The PCM uses the data from the engine coolant temperature sensor to control the air-fuel ratio, ignition spark timing, cooling fan operation, and other components of the emissions control system.

car engine overheating
An overheating engine is a possible cause of code P0115.

What are the Possible Causes of the P0115 Code?

DTCs, such as the P0115 code, have a number of possible causes. This is mainly due to the fact that DTCs themselves can only point to the nature and location of the potential issue and not the main cause itself. Listed below are some of the possible reasons why the P0115 code sets:

What are the Common Symptoms of the P0115 Code?

When there is a potential issue with sensors or sensor circuits, the vehicle’s computer system stores information about the issue as a diagnostic trouble code. The computer may also send a signal to turn the malfunction indicator lamp (MIL) on. In some cases, an activated MIL is the only indicator that there is a problem.

However, you may observe other signs if you encounter other DTCs. If you’re dealing with the P0115 code, you may notice the following symptoms:

engine hard starting
A hard starting engine might indicate that your car computer has logged code P0115.

How to Diagnose the P0115 Code

In order to fix DTCs, such as the P0115 code, you’ll need to conduct a thorough diagnosis. Diagnostic trouble codes can only point you to the nature and the location of the potential problem, not the issue itself. For you to formulate an effective and long-term solution, you’ll have to determine the exact root cause.

There are a lot of sources to help you troubleshoot DTCs. Vehicle-specific repair manuals and databases are the best sources because they have detailed repair instructions as well as helpful diagrams and illustrations. Online materials such as how-to videos, blogs, and online training tools are also quite helpful.

How to Fix the P0115 Code

Fixing DTCs takes time and effort. First, you have to determine what triggered the code in the first place. Doing this requires you to narrow down the list of possible causes until you reach the main issue.

Second, you have to note that vehicles are built differently so terminology, DTC setting conditions, and repair instructions will differ depending on the make. For example, the P0115 on Nissan vehicles puts the engine in a fail-safe mode while the P0115 ion Toyota vehicles doesn’t.

Repair manuals can help the seasoned DIYer to fix the issue. However, if you’re not confident in your DTC repair skills, it’s best to leave the job to a certified mechanic and/or technician.

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