See a dealer
Under the thermostat
the coolant sensor is in the radiator on the passanger side the oxygen sensor is in the exhaust system on the manifold and the pipes and sometimes both
On a 2001 Monte Carlo it is located on the radiator just below the radiator cap.
If coolant full could be a bad sensor
Check coolant level in recovery tank Perhaps a bad sensor. Sensor located in coolant recovery tank
Where is hood open sensor on 2006 Monte Carlo
where is the crankshaft position sensor on a 2003 monte carlo
Look where the thermostat is attached to the intake manifold
The low coolant sensor is bad or disconnected.
Did you change the radiator? If you did you might have the wrong one,without a full provission for the sensor. If you did not the plug might be disconnected or faulty.
has the red coolant in a 2005 monte carlo been changed since reports on it deteriorating the head gasket?
Depending on the year of the Monte Carlo the 02 sensor could be installed in several places on the exhaust. The 02 sensor screws in. You may need a special socket to remove it, just unscrew the sensor and screw the new one in.