i keep gettin this code 15 min after i start the car after it gets cold what is it and how do i fix it?

on a 2002 ssei

That says the car is detecting low coolant temperature. Could be a problem with the coolant temperature, or the sensors that detect the temperature. Possible causes are a defective thermostat (stuck open), low coolant level, defective engine coolant temperature sensor or a defective intake air temperature sensor. All easy to check and repair if required.

Read the write up: https://www.gmforum.com/obd-ii-trouble-shooting-153/p0128-284065/