Check Engine Light Code P0125 on my 99 Chevy Tahoe?

More than likely the t-stat is bad or has been removed, or the coolant is low. The P0125 means that the vehicle has not gotten up to closed loop temperature in a given time frame. Check the coolant level and t-stat operation first.

For 1999-2001 Tahoe P0125 code is "Insufficient coolant temperature for closed loop fuel control."

What does it mean? I have no idea. Sounds like a coolant problem.

p0125 is ect code, ect= engine coolant temperature sensor, its mounted on driverside cylinder head, look to see if the wires have melted against exaust, may be able to repair or may have to replace, the code ie closed loop which means circuit is complete but out of range due to wires maybe or just faulty, open would mean unpluged or broken wires or faulty sensor, make sure coolant system is full

i do tons of these. check the coolant level first. if it is low, have the coolant leak fixed and re-evaluate the concern. if the coolant level is correct, have the thermostat replaced.

the computer monitors the amount of engine run time and expects to see normal operating temperature within a certain amount of time. if the thermostat is stuck open, which is your case, then the vehicle will take twice as long to reach temperature, and the code fails.

It may also be the intake manifold gasket has a leak with my tahoe had the same issue replaced plugs and all the coil packs and it turned out to be a leak from the lower intake manifold gasket a very common problem with all chevys

Sounds like the coolant temp. sensor is bad...I don't know the price though.

yup listen to mariahle it is the the thermostat failing ,engine not reaching temp