Having trouble locating ect sensor 1999 deville, where is it

I can visual see it under hood. so open hood and look

If you mean ECT (Engine coolant temperature) sensor, yes it can.
The ECT is responsible for turning on & off the radiator cooling fan.
However an ETC (Electronic traction control) sensor typically wouldn't cause the engine to overheat. However if there is a code in the engine computer it can turn off the traction control. So if the ETC is turning off it may be a result rather than a cause.
You'll need to check for codes in the engine computer & if there is one for the temperature sensor you most likely will need to replace it but you'll also need to check the coolant level. If it is low you obviously have a leak.
FOOT NOTE: This engine is well know for its HEAD GASKETS leaking coolant. If you are having persistent overheating conditions & can't seem to locate the cause ie; water pump, radiator, hose ect. you most likely will need to have the head gaskets replaced... & that isn't cheap.

Hope this helps.
FarrouT!

It means you should try replacing the engine coolant temperature sensor as it has probably failed (it's located on the driver's end of the engine at the middle about half way down).

If you are refering to the Engine Coolant Temperature (ECT) sensor,it is located on the right rear of the engine below the exhaust gas recirculation (EGR) valve.

HINT: If your Deville is equipped with the analog instrument cluster and the temperature gauge is working, or if you have the digital instrument cluster and the driver information center (DIC) has been diplaying messages telling you that the engine is hot, the problem with your engine cooling fans is NOT the sensor.

Some thing too check:

Make sure coolant level is up to line and clean (not dirty, may need to be flushed out).

Make sure air flow through the out side of radiator is clear (dirt, leaves, ect..) .

Make sure electric fan is working properly (not running slow).

Check radiator cap, (no gasket tears).

Could be thermostat going bad ?

Could be coolant temperature sensor/switch (from computer) going bad?

Check radiator hose(s) (too soft, may collapse)?

ECT.............Hope tis was some help??.

Click over pic for zoom...



Fig. Showing the location of MAP Sensor and other components on the front of the engine: 1. Manifold Absolute Pressure (MAP) Sensor; 2. Idle Air Control (IAC) Valve; 3. Engine Coolant Temperature (ECT) Sensor; 4. Throttle Position (TP) Sensor



Fig. Engine coolant temperature sensor (1).

you have 4.6l engine ect sensor located below the egr valve. now if you have 4.9l engine ect located on the thermostat housing.

in the left rear corner of the engine, below the exhaust gas recirc valve..has two wires black and yellow

Trouble Code: P1258 (4.6L V8 VIN 9 Auto)
Engine Metal Over-Temperature Protection
Number of Trips to Set Code: 1
OBD II Monitor Type: CCM Details
Indicators: MIL Details

• CCM Details
• MIL Details

Trouble Code Conditions:
DTC P0117, P0118 and P0125 not set, Engine started; and the PCM detected the ECT sensor indicated more than 270ºF for 10 seconds. The PCM uses the ECT sensor to detect if the engine is running too hot (when the ECT sensor is over 268ºF). If the engine is overheated, DTC P1258 will set. The PCM will disable 2 groups of four cylinders by turning off the fuel injectors. By switching between the two groups of cylinders, the PCM is able to reduce the temperature of the coolant and lower the temperature.

Possible Causes:

• Engine cooling system problem (test the cooling fan operation)
  
• Engine coolant level is low or the mixture is not correct
  
• ECT sensor is out-of-calibration or "skewed"
  

disconnect the negative battery cable.
Pull the harness of the sensor.
Drain about 1/4 of the radiator fluid.
Place a rag under the sensor and use a wrench to remove and replace the sensor.