Question about 1991 Lexus LS 400

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My lexus ls400 1991 the two electri fan all time is on

My lexus ls400 1991 the two electric fan all time is on, air condition is off and the engine is cold.

Posted by Anonymous on

  • Anonymous Jul 21, 2010

    I tried pulling sensor from radiator but there is no change the fans still run.

    Also have a new/good relay however when I insert it I notice it remains shut and will not open as if it's not getting any current.

    Is there any other components to check? I appreciate your help. Thanks



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Walt Ziemke

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Check the thermostat to see what temp it is opening at?? should be around 160- 180 degrees..

Posted on Jul 19, 2010


Kirk Augustin

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Either the temperature sensor on the radiator, or the relay is bad.
Pull a wire off the temperature sensor on the radiator.
If it stops the fans, then the sensor is bad and the relay ok.

Posted on Jul 19, 2010

  • Kirk Augustin
    Kirk Augustin Jul 22, 2010

    If the old relay was bad and stuck on, then removing the old relay should allow the fan to shut off.
    Then plugging the new/good relay in should allow the fan to remain off, until the sensor on the radiator gets hot enough to cause the relay to go on.
    There is no computer or control system to reset.
    There is just the temperature sender in the radiator that acts like an on/off switch, and the relay that allows the temperature sender to control the fan without getting burned out. If not for the relay, too much current would have to go through the sensor switch, and it would rapidly burn out from the arcing, because the fan motor draws so much current.



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