Trouble Code Info: P0128 (Coolant Temperature Below Regulating Temperature)


The internal combustion engine of a vehicle generates a vast amount of heat. The two liquids responsible for cooling the engine off are the oil and coolant. The latter is ultimately more important for this task. But if the coolant is going to do its job successfully, it needs to stay at a certain temperature and not overheat itself either. A functioning cooling system will be able to keep the coolant at a regulating temperature of between 194°F and 212°F. This is considered the normal temperature range for coolant in an engine.

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If certain components of the cooling system were to malfunction, it would jeopardize the normal temperature range of the coolant. If the coolant temperature is too low, it will usually cause the engine to consume more fuel and produce more carbon emissions. If the temperature is too high, the engine will overheat and then ultimately be destroyed. For these reasons, it is important that the coolant stays at the right temperature.

Trouble Code P0128

If the regulating temperature of the coolant falls below 194°F, it will be detected by the powertrain control module. This will cause the module to generate trouble code P0128 as an indicator that the temperature is dropping. However, unless your vehicle will display the trouble code on your dashboard, you are not going to realize this problem exists right away. The first sign of a problem will be the Check Engine light illuminating on the dashboard. You will also notice your fuel being consumed a lot faster by the engine.

At this point, you will want to scan your vehicle’s powertrain control module to see the trouble code for yourself and verify that you have low coolant temperature. Once you verify this, you need to figure out the cause of the problem. The most likely scenario is that your thermostat is not working properly.

Read also: Trouble Code Info: P0456 (Evaporative Emission System Leak Detected)

For instance, if your thermostat has trouble closing and it just stays open all the time, then the coolant will keep entering the radiator to get cooled down. It doesn’t even matter if the coolant is already cold either. The purpose of the thermostat is to close and block the flow of coolant at times when the coolant doesn’t need to be cooled by the radiator. But if the thermostat is always open, then it cannot do this. As a result, you will likely see trouble code P0128 be generated by the powertrain control module.


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