P0126 Fault Code

Long Description

Fault code P0126 represents an issue with the engine coolant temperature (ECT). It is logged when the powertrain control module (PCM) has detected that the coolant temperature is insufficient to safely run the engine.

The engine coolant is responsible for ensuring the engine does not overheat. It also aims to keep the temperature at an optimum of roughly just below boiling point. This is done to increase performance and efficiency.

The ECT sensor continuously monitors the coolant to ensure that it is properly performing and meeting both of these goals.

This code can be logged by any manufacturer. However, Jeep and Mazda are by far the most commonly searched when it comes to P0126. In fact, this is a very common code for Mazda vehicles, which resulted in the Japanese manufacturer issuing a technical service bulletin on the problem.

Other Signs of This Problem

There can be some serious symptoms when it comes to any engine coolant temperature issues.

The most obvious sign of this issue will be the presence of the Check Engine light on the dashboard. In some cases, the vehicle will also enter limp mode until the problem is resolved.

Another fairly common symptom is that the temperature gauge will display an abnormal reading. This can include rising too quickly or too slowly, as well as not reaching a stable temperature.

The performance of the vehicle may also degrade. The most likely outcome will be increased fuel consumption.

Be sure to look out for additional codes that can relate to this problem. These can include P0115 to P0119 and P0125 to P0128.

What Could Be The Problem?

There are a huge number of potential causes when it comes to a broad cooling problem like this.

A faulty thermostat can be one of the most likely culprits.

In terms of engine coolant, old or contaminated coolant can also be a primary cause. Additionally, a vehicle with the incorrect coolant level can suffer from this fault code.

Another common cause for this problem is a faulty ECT sensor. In addition to this, a faulty intake air temperature (IAT) sensor can also lead to this type of issue.

Electrical faults in the various sensor circuits can also cause this issue. These can include damaged wires or loose connections.

Fixes

There are a number of potential fixes for this issue because of the broad nature of the fault code.

One of the easiest and quickest fixes for this problem is to drain the engine coolant and replace it with fresh engine coolant to the level specified by the manufacturer. It is also a good idea to check the cooling system for leaks if the coolant level is low. Any leaks need to be fixed.

Another relatively easy step is to replace a faulty thermostat.

If any of the relevant sensors like the ECT or IAT are defective, they should be replaced. These sensor circuits also need to be checked for electrical faults and fixed accordingly.

Seriousness

Fault code P0126 should be considered a serious problem. Any issues with the engine’s cooling system can lead to serious damage if ignored for too long. It can also lead to a number of driveability issues.

It is strongly recommended to have this fault code fixed immediately.