DTC P1258: Engine OVERTEMPERATURE: Description
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Sonoma, 2002 GMC Safari, 2002 GMC Jimmy, 2002 Chevrolet S10 Pickup, and 2002 Chevrolet Blazer. However, it is still accessible from the selected car via links, so may be relevant.
The PCM uses the ECT sensor to monitor the engine for an over temperature condition. This condition occurs when the coolant temperature is above 270°F (132°C). When an over temperature condition is present, DTC P1258 will set. The PCM will alternately disable 4 injectors. By alternately disabling 4 injectors, the PCM is able to reduce the temperature of the coolant.