Check engine light is on . need to know where the thermostat is located

How do you know the sensor is bad? Have you checked the coolant temperature using an external temperature gauge?
Best bet is to replace both the thermostat/housing and the temperature sensor, they are not that expensive, and are located in the same area of the engine.

Coed 17-Engine is cold to long, check your thermostat.
Follow the upper radiator hose to the engine to locate
the thermostat. Recommend disconnecting negative
battery cable before replacing it. A repair manual is
handy for the replacement procedure. While you're at
it, check the hoses for replacement if needed.

No heat could be caused by a number of things, but first check the coolant and make sure that its full, next i would check the thermostat if its opening to soon its not allowing the engine to get hot most likely you would have a check engine light on with a code if this was the case being your car is post 96 and OBD2, another possible cause could be a blockage inside the heater core not allowing the hot coolant to cirrculate, if your coolant is dirty it may require a reverse flush of the entire cooling system to try and remove the dirt/rust.

2.2L Engines - 1987-91 VEHICLES



Fig.: Thermostat location and mounting - 1987-91 2.2L engines




2.8L and 3.1L Engines



Fig.: After unfastening the retaining bolts, remove the outlet and lift out the thermostat - 3.1L engine shown


Hope helps (remember rated this).

The thermostat is located where the upper radiator hose connects to the engine.

Never heard of a thermostat sensor. There is a diagnostic code that wil lbe set if the engine computer observes that the thermostat is not allowing the engine to reach operating temperature quickly enough. This code is based on information sent by the engine coolant temperature sensor. 99.9% of the time a new thermostat solves the problem. Use an AC Delco thermostat.

Check this location.
Between the alternator and A/C compressor, on the top. The other thermostat with vent holes goes toward the rear of the engine.
I believe the temp ratings are different for each.
Let engine cool before working on it.
Clean up an spilled radiator fluid. It will destroy pets liver in 24 hours if they drink it.

WHAT YEAR & ENGINE

Here is the definition of the code in GM manual:
P0128 - Coolant Thermostat Below Thermostat Regulating Temperature, this indicates the engine is running cold, u need a thermostat

HI..
The Speed sensor on your Honda Accord 97.
Is located on the Transmission.
If you follow the Lower Radiator hose from the rad to the engine.
The hose end on the Thermostat housing.
OK.. Just on direction of the thermostat housing .
Under the housing you Will see on the transmission the Speed sensor, with a connector of 3 wires. Is the only sensor at this
Part of the Transmission..

Ok. I hope this work on your question.
Thank you for use fixya..