Next to the thermostat. you will see it when you remove the hose
If you mean for Coolant level sensor it is on the bottom of the plastic coolant dish on the passenger side of the car.
I have 1993 Volvo 960 and the coolant senor is located on the back of the block ( next to fire wall) The access is very difficult because the are two water hoses and some electrical wires right next to it.
I'm not sure what you're asking, but if you mean that you are getting an OBD-II diagnostic code of P0128 from your Volvo S40, that code corresponds to a problem with coolant temperature. On a first generation Volvo s40 (99-04), this usually means that the thermostat or electronic coolant temperature sensor are malfuctioning or have failed.
Try looking on the EGR valve underneath the intake manifold.
in mirror
If a complete tune-up (with new ignition wires, plugs, air filter, cap, rotor) does not improve gas mileage, replace the coolant temperature sensor. The sensor is located under the intake manifold. Cost is about $39.00. Check the shape of the wiring socket to make sure you get the right sensor.
On the passenger side of the engine compartment there is a surge tank remove that and the sensor is in the bottom. It will be the clear plastic tank where you add Coolant.
I posted pictures on the location and replacement of an ambient temp. sensor for a 2001 S40. Google "ambient temperature sensor location/replacement" or go to Matthew's Volvo site and search there.
It is located in the intake pipe between the MAF sensor and the throttle.
where is the crankshaft position sensor located on a 2002 Volvo S60 2.4 engine
it's on the radiator, just pull the wires and unscrew it.
where is the crankshaft position sensor located on a 2002 Volvo S60 2.4 engine