Cooling fans not running

Tiny
GW.WILSON
  • MEMBER
  • 1999 CADILLAC DEVILLE
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 133,395 MILES
Running over 200 degrees when sitting at stop light or stop and go driving. So I looked under the hood and seen the radiator fans were not running. How do I fix this problem?
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Monday, April 17th, 2017 AT 4:22 PM

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Tiny
STEVE W.
  • EXPERT
You need to determine which part or parts have failed. The problem could be the fan relays, temperature sensor, fuses. Start by checking the fuse that powers the fans.
It is a 50 amp maxi fuse in the right hand fuse block. Then the AC fuse 10A in the fuse block under the hood. Next would be to use a good scan tool to control the relays to test them and the fans. It's possible to test them manually but the scan tool method tests all the parts and wiring at one time. See the attached wiring to see the way the circuit works.
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Monday, April 17th, 2017 AT 6:23 PM
Tiny
WRENCHTECH
  • EXPERT
You are looking for a problem that does not exist. There is nothing wrong with your fans. They are not programmed to run anywhere close to 200 degrees.

The PCM will command fan operation when:

Low speed fan operation.
Engine coolant temperature exceeds approximately 106 C (229 F).
Transmission fluid temperature exceeds 150 C (302 F).
A/C operation is requested.
After the vehicle is shut off if the coolant temperature at key-off is more than 151 C (304 F) and system voltage was more than twelve volts. The fans will stay on for approximately three minutes.

The fans will switch from low to off when the coolant drops below 102 C (216 F).

High speed fan operation.
Engine coolant temperature reaches 112 C (234 F).
Transmission temperature is more than 151 C (304 F).
When certain DTCs set.

The fans will switch from high to low (except DTCs set) when the coolant drops below 106 C (229 F).
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Tuesday, April 18th, 2017 AT 5:10 AM

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