What is the easiest way to remove and replace the engine coolant temperature (ECT) sensor on a 99 Cadillac Deville, 4.6L

What engine ? 3.6 or 4.6
Engine Coolant Temperature (ECT) Sensor (LH2)
In the rear side of the right cylinder head
Engine Coolant Temperature (ECT) Sensor (LY7)
In the left cylinder head near the center cylinder

P0119 Cadillac Engine Coolant Temperature Circuit Intermittent
Possible causes - Low engine coolant level
- Faulty Engine Coolant Temperature (ECT) sensor
- Faulty engine coolant thermostat
- Engine Coolant Temperature (ECT) sensor harness is open or shorted
- Engine Coolant Temperature (ECT) sensor electrical circuit poor connection What about the obd code? The Engine Control Module (ECM) detected an erratic signal from the engine Coolant Temperature (ECT) sensor during the system monitor test Symptoms - Engine Light ON (or Service Engine Soon Warning Light) P0119 Cadillac Description The Engine Coolant Temperature (ECT) sensor is used to detect the engine coolant temperature. The sensor modifies a voltage signal from the Engine Control Module (ECM). The modified signal returns to the ECM as the engine coolant temperature input. The sensor uses a thermistor which is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases.
P119 or P0119 ?

P119 - Shorted Fuel Injector Problem
or

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

Try looking screwed into the radiator.

NOTE Use care when handling the ECT sensor. Damage to the coolant sensor will affect the operation of the fuel control system.

NOTE The engine coolant temperature sensor is located on the intake manifold water jacket or near the thermostat housing. On the 4.6L engine, the coolant temperature sensor is located on the rear cylinder head, at the cruise control servo bracket. It is necessary to drain coolant from the cooling system to a level below the sensor, prior to sensor removal.

1. Disconnect the negative battery cable.
2. Drain the coolant level below the height of the ECT and recycle the engine coolant.
3. Detach the electrical connector at the sensor.
4. Remove any obstruction to access the ECT.
   1. On the Catera, this would include removing the intake plenum and the intake bridge.
   
   
5. Using a deep well socket, remove the sensor.

To install:

1. Coat the threads of the new sensor and install it in the engine. Tighten to 15 ft. lbs.
2. Install the electrical connector.
3. Refill the system with coolant.
4. Connect the negative battery cable.

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.

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).

4.2L Engine To Remove:

1. Disconnect the negative battery cable from the battery.
2. Drain the coolant from the engine.
3. Disconnect the engine coolant temperature (ECT) sensor connector. Engine coolant temperature sensor removal and installation
   
   
4. Remove the engine coolant temperature (ECT) sensor from the engine.

To Install:

1. Apply thread sealer P/N 12346004 or equivalent to the engine coolant temperature (ECT) sensor threads.
2. Install the engine coolant temperature (ECT) sensor into the engine. Torque the sensor to 12 ft-lb (16 Nm).
3. Connect the engine coolant temperature (ECT) sensor connector.
4. Refill the engine with coolant.
5. Connect the negative battery cable to the battery.

5.3L & 6.0L Engines To Remove:

1. Drain the coolant from the engine.
2. Disconnect the engine coolant temperature (ECT) sensor connector. Engine coolant temperature sensor removal and installation
   
   
3. Remove the engine coolant temperature (ECT) sensor from the left cylinder head.

To Install:

1. Apply thread sealer P/N 12346004 or equivalent to the engine coolant temperature (ECT) sensor threads.
2. Install the engine coolant temperature (ECT) sensor into the left cylinder head. Torque the sensor to 15 ft-lb (20 Nm).
3. Connect the engine coolant temperature (ECT) sensor connector.
4. Refill the engine with coolant.

Maybe this will help . although this is from a 1997 Caddy.


Cadillac DeVille Engine Coolant Temperature (ECT) Sensor Location