The vehicles are equipped with a Engine Coolant Temperature (ECT) whose signal is sent to the PCM (Powertrain Control Module) to optimize the operation of the vehicle.
For the correct operation of the engine, it is necessary that it reaches a particular temperature range. If in a period of time the vehicle does not reach this operating temperature, the DTC code P0126 OBDII is set, so the warning or Check Engine light will illuminate.
It should be noted that this code will not be set immediately after the engine starts. It is only set after a period of time, which has been programmed by the PCM. Although that time period varies by manufacturer, ambient temperatures can influence that period.