My Daughters 1999 ZX2 just put the CEL on. Went to AZ and found code p0125 , insuffecient engine coolant temp. I will look into the coolant sensor or maybe the thermostat. Car only has 37,000 miles. Anyone ever dealt with this code? What was your fix?

it's probly the temp snr .. there sould be a explaination in the service book on how to check it if you dont have acces to that kind of info .. just replace the snr .. it shounld be that expensive anyway

Checked out the problem a little more. When I drove the car I noticed the temp gauge was not coming up to a normal reading after some extended driving. I checked the Temp Sensor when it was cold and warm according to the specs in the Haynes manual and they were right where they should have been. I had approx 5 VDC at the connector also. So I went back to Auto Zone and got a new thermostat and installed it. I reset the computer to rid the CEL and so far it has stayed off. The temp gauge now reads in the middle like it should. Partsman at AZ kept insisting that a faulty thermostat could not cause this code.

if you find somebody with alldata, it give you the test readings for the ect sensor in ohms. you will need a dvom meter to test.

i should have read further, yes a themostat that is stuck open or that is opening to quickly can cause this code.the ecm is not seeing enough temp in a certain amount of time. it can also cause a rich running condition at startup until the ecm sees enough temp

I did check the sensor's ohm values according to the Haynes manual. The hot and cold readings are different because it is a thermister, which varies the ohm reading(resistance)when the temp rises. Like I told the counter person at AZ, it could not be the sensor probably the thermostat. I still have not had any trouble with the car since changing it.