My 1998 pontiac firebird service engine light came on and my OBD11 scanner produced 2 trouble codes PO125 ( insufficient coolant temperature for closed loop fuel control.the 3800V6 engine over heating and heater produces cold air only.l replaced the themostat and the(ECT)engine coolant temperature sensor but service engine light still on and scanner trouble code PO125 still on.What else would cause these engine over heating problems and heater not producing hot air, triggering a PO125 code insufficient coolant temperature for closed loop fuel control OBD11 trouble code and service engine soon light?

I hope you realize that the po125 DTC code does not necessarily mean that you have a problem with the cylinder head temperature [CHT] sensor or the Engine Coolant Temperature [ECT] sensor.

It only means that the coolant temperature is too low for closed loop operation.

Other issues that may trip a DTC po125,

• Insufficient warm up time
• Low engine coolant level
• Leaking or stuck open thermostat

I would clear the code and see if it comes back- since you won't experience any difference in engine operation anyway.

You'll need to perform a continuity test on the sensor, when the engine is cool and then again after warming up the engine.

Then you'll want to take voltage readings on the wire harness that goes from the ECT back to the GEM.
You may find that the wire harness from the sensor to the GEM may be shorting out.

However, I would think that, if anything, the thermostat would be the culprit and malfunction before a faulty sensor.

You'll find the sensor under the upper radiator hose where the thermostat housing is mounted on the engine block. It may be obscured by the alternator.

And if you don't mind my 2 cents worth of friendly advice, either purchase a Chilton or Haynes repair manual from your local auto parts store or online.

Good luck on your project.

code po125 refers to insufficient coolant temperature for closed loop fuel control causes ---wiring--cooling system---coolant thermostat--ECT sensor ---ECM. Check the level in the radiator. take it to a specialist mechanic for your car

Here's a link,may be your coolant temperature sensor. P0125 OBD II Trouble Code Insufficient Coolant Temperature for Closed Loop... Here's a video of where it's at Coolant temperature sensor location 2003 Expedition 5 4

P0125 - Insufficient Coolant Temperature for Closed Loop Fuel Control Possible causes - Harness or connectors (The sensor circuit is open or shorted.)
- Engine coolant temperature sensor may be faulty
- Thermostat may be fault (most common cause)
P0650 - Malfunction Indicator Lamp Control Circuit Malfunction (Check Engine light)

Symptoms - Engine Light ON (or Service Engine Soon Warning Light)
Possible causes - Harness or connectors for the MIL (Check Engine Light) circuit is open or shorted
- MIL bulb may be faulty
- Faulty ECM

DTC P0125 - Insufficient Coolant Temperature For Closed Loop Fuel Control

This means that the engine coolant temperature (ECT) sensor indicates that the engine has not reached the required temperature level to enter closed-loop operation within a specified amount of time after starting the engine.

Symptoms: You will likely not notice any drivability problems.

Causes: A code P0125 may mean that one or more of the following has happened:
* Insufficient warm up time
* Low engine coolant level
* Leaking or stuck open thermostat
* Faulty coolant temperature sensor

Possible Solutions: The simplest thing to do is to reset the code and see if it comes back.

If the code comes back, the problem is likely going to be the result of the above causes (faulty thermostat, faulty ECT sensor, or a low coolant level).

Hope this helps (remember to rate this answer).

A code P0125 may mean that one or more of the following has happened:

• Insufficient warm up time
• Low engine coolant level
• Leaking or stuck open thermostat
• Faulty coolant temperature sensor

The simplest thing to do is to reset the code and see if it comes back.
If the code comes back, the problem is likely going to be the result of the above causes (faulty thermostat, faulty ECT sensor, or a low coolant level) theres your answer need more help just tell me

PO125 INSUFFICIENT COOLANT TEMPERATURE FOR CLOSED LOOP CONDITIONS.POSSIBLE CAUSES - LOW COOLANT LEVEL - STUCK OPEN THERMOSTAT OR FAULTY ENGINE COOLANT TEMPERATURE SENSOR. DID NOT SEE CODE P1139.

P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control
Replace your coolant temp sensor.Be sure to double check your coolant level and does the engine reach an operating temp(about halfway on the guage)in a normal time?! If it does, the temp sensor for the computer needs to be replaced.

Insufficient coolant temperature. Probably a bad thermostat, unless you are experiencing near zero temperatures in your town. If that's the case, chances are the light will go out when the weather warms up.

I would have the OBD II scanner clear the codes. Then if the code still pops up, I would have the coolant temperature sensor looked at.