P0115 Fault Code

Long Description

Fault code P0115 is logged when the engine control unit (ECU) has detected a malfunction with the engine coolant temperature (ECT) sensor circuit.

This occurs when the readings from the sensor are out of the predetermined allowable range, being either too high or too low.

The ECU monitors coolant temperature carefully for a host of reasons. One of the most important is to prevent overheating as it can severely damage various components in the engine.

Additionally, the ECU uses coolant temperature to adjust the air-fuel mixture entering the combustion chambers, ignition spark timing, cooling fan operation, and emissions control.

Toyota, Nissan, and Opel/Vauxhall are among the most commonly searched manufacturers when it comes to fault code P0115.

Other Signs of This Problem

A malfunctioning ECT sensor can lead to numerous noticeable issues with how the vehicle behaves.

One of the most obvious signs is the Check Engine light is illuminated – along with an OBD2 reader diagnosing that light to be the P0115 fault code. In some cases, the Overheating warning light will be illuminated.

The engine will also behave erratically in most instances. This can include very poor performance, hard starting, and engine dying.

The vehicle’s cooling systems will also perform poorly. This can include overheating and the fans working strangely. For instance, the cooling fans may be running at full even when the engine is cold.

There may be other fault codes relating to the engine coolant system as well. Look out for codes like P0116, P0117, and so on up to P0128.

The engine may also run excessively lean or rich. This can result in black smoke being emitted from the tailpipes.

What Could Be The Problem?

Like with any sensor-related issue, the cause can come from the sensor and its corresponding circuit or from the system it is monitoring.

It is possible that the ECT sensor has become damaged or faulty, providing incorrect values to the ECU.

Additionally, damaged or loose connections or wires in the ECT sensor circuit can also be the cause. A short or open circuit can also lead to this fault code.

Within the cooling system itself, it is possible that a low coolant level or air in the cooling system can cause these erratic readings.

The engine overheating is another reason for excessively high readings. However, this will come with other fault codes and warning lights.

Fixes

Fixes should focus on repairing a damaged or faulty ECT sensor first. If the issue persists, other steps should be taken.

The ECT sensor should be cleaned of any moisture or contamination and tested. If it is faulty, it needs to be replaced. The ECT connector should also be replaced if faulty.

Any damaged wiring or connections should also be repaired. Ensure there are no loose connections in the sensor circuit.

Coolant should be topped up if it is running low. Additionally, air must be purged from the cooling system if it is detected.

Seriousness

Fault code P0115 should be considered a severe problem. There is a great risk of damaging expensive components in the engine while operating the vehicle while there is an ECT sensor malfunction.

Additionally, driveability will be significantly hampered in most instances.

It is a good idea to have this issue resolved immediately.