99 cadillac de ville

If you make a jumper wire and jump the load side of the relay and the fans work, it might be the relay or it might be the control side of the relay not getting the signal from the temperature switch. If you jump the load side and the fans don't work it's either the fan motors or a wiring issue between the relay and the fans.

Cooling fan switch ?????? Has a engine coolant temp. sensor , That inputs info to the PCM/ECM - engine computer ! The PCM / ECM interpits the voltage signal from software programmed into it as to what temp . of the coolant is . When the engine coolant temp. reaches
The PCM commands the low-speed fans ON under the following conditions:
• The engine coolant temperature exceeds approximately 106°C (223°F).
• The transmission fluid temperature exceeds 150°C (302°F).
• The A/C pressure reaches 199 psi (1372 kPa).
The cooling fans will switch from low to OFF when the coolant temperature drops below 102°C (216°F).
The PCM commands the high-speed fans ON under the following conditions:
• The engine coolant temperature reaches 112°C (234°F).
• The transmission fluid temperature is more than 151°C (304°F).
• The A/C pressure reaches 260 psi (1792 kPa).
• Certain DTCs are set.
The cooling fans will switch from high to low, except when DTCs are set, when the coolant temperature drops below 106°C (223°F).

The PCM turns on the cooling fans by energizing three different relay's .
Watch this video
Relay Driven Dual Cooling Fan Diagnostics

Two cooling fans controlled by three relay's . If only one fan is working ,that could be a problem .
Coolant Level Sensor Description
The coolant level sensor monitors the coolant level in the cooling system and indicates if the coolant is low. This sensor is located at the base of the radiator surge tank and is not serviceable.
CHECK COOLANT LEVEL (2)
The IPC receives a discrete input from the engine coolant level switch. The engine coolant level switch is normally closed. When the engine coolant is low, the engine coolant level switch opens. When the IPC receives an open signal from the engine coolant level switch, the IPC displays the message on the DIC.

Relay Driven Dual Cooling Fan Diagnostics There are using a pontiac , by your cadillac is the same .

Look for the silly stuff. Check for things blocking off the radiator, coolant level, water pump belt, etc. If none of those help, check the cooling fan, coolant temperature sensor, fan relay and fan fuses. If everything there is working, consider a stuck thermostat, an obstruction in the cooling system itself or a failed water pump. Kind of a long shot but engine timing can also make it run hot. Hope this helps.

210-230 degrees usually .

Thank you for the inquiry.
RADIATOR FAN CONTROL
Fan control is accomplished two ways. A pressure transducer on the compressor discharge line sends a signal to the Powertrain Control Module (PCM) which will activate the fan. In addition to this control, the fan is turned on by the temperature of the coolant which is sensed by the coolant temperature sensor which sends the message to the PCM. The fan will not run during cranking until the engine starts no matter what the coolant temperature is.

CAUTION: The solid state fan relay is attached to the left frame rail near the lower radiator support. The relay bracket, and fastener are used to dissipate heat from the relay. Ensure the relay is properly attached to prevent the following:

Intermittent engine overheating.
Relay "thermal" shutdown, or relay damage.
Hope helps; keep us updated and remember to rate this answer.
Kind regards,
TF

Removal & Installation To Remove:

1. Before servicing the vehicle refer to the precautions at the beginning of this section
2. Remove or disconnect the following:
   • Engine coolant into a suitable container to a level below the ECT sensor
     
     
   • ECT sensor harness connector (A)
   • ECT sensor

To Install:
NOTE: Use care when handling the coolant sensor. Do not drop damage to the coolant sensor will affect the operation of the fuel control system.
NOTE: Replacement components must be correct for the application. Components requiring the use of the thread locking compound, lubricants, corrosion inhibitors, or sealants are identified in the service procedure. Some replacement components may come with these coatings already applied. Do not use these coatings on components unless specified. These coatings can affect the final torque which may affect the operation of the component. Use the correct torque specification when installing components to avoid damage.

1. Coat the sensor threads with GM P/N 1050805 sealer or equivalent
2. Install or connect the following:
   • ECT sensor
     1. Torque to: 15 lb-ft. (20 Nm)
   • ECT sensor harness connector
   • Engine coolant
3. Start the engine then idle until normal operating temperature is attained.
4. Recheck coolant level and top off as needed.
5. Test drive the vehicle.

--- I couldn't find a reference for the 'fan coolant relay switch' although I'm sure there is one on this car.

2.4 ENGINE COOLANT SENSOR IS LOCATED ON THERMOSTAT HOUSING THE 3.3 AND 3.8 ENGINE COOLANT TEMPERATURE SENSOR IS LOCATED LOWER INTAKE MANIFOLD.ALSO CHECK COOLANT FAN FUSE AND RELAY.FUSES RELAYS LOCATED LEFT SIDE OF THE ENGINE COMPARTMENT.

This link has a diagram showing the location of the relay: http://autorepair.about.com/library/faqs/bl581g.htm

The Pulse Width Modulated (PWM) radiator cooling fan relay is located behind the front bumper fascia below the right head lamp.

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


Cadillac DeVille Engine Coolant Temperature (ECT) Sensor Location