1999 Buick Century Cooling fan issue

  • 3.1L
  • 6 CYL
  • FWD
  • 69,500 MILES
My cooling fans do not want to come on when the temp begins to climb, until it reaches an unsafe temperature range above normal. I have replaced the Temperature Sensor with no luck. The issue remains. The dual fans come on when the a/c is turned on, but still they will not come on due to engine temp until like I said, when engine reaches an unsafe temperature. My book shows 3 relays, Relay 1, relay 2 and Relay 3, they are identical, why does it need 3 relays for dual fans wired in conjunction and why wont they come on at the correct water temp?
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have the same problem?
Thursday, May 8th, 2014 AT 1:49 PM

1 Reply

First of all, temperature gauges are notoriously inaccurate. They are most useful when you know from plenty of experience what "normal" is, and you notice when something abnormal is occurring. Second, a lot of GM cars are designed for the fans to not turn on until coolant temperature gets well above the boiling point of water, 212 degrees F. A switching point if 220 degrees is common and acceptable. Third, there are usually two different coolant temperature sensors; one for the Engine Computer which controls the radiator fans, and one for the dash gauge. It's common to find a discrepancy between them. To know for sure if there really is a problem, you need a scanner to view live sensor data. That will show you the actual coolant temperature.

The reason for the multiple relays is you may have a high-speed relay and a low-speed relay, and there could be a third one that turns the fans on when the AC compressor turns on. The low-speed relay is used when the manufacturer wants less noise to be heard and lower air flow is sufficient. You may not hear the fan turn on low speed if the hood is closed.

Also, a scanner will allow you to command the relays to turn on and off. That will let you verify the circuitry is operating properly.
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Thursday, May 8th, 2014 AT 3:10 PM

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