Question about GMC Sierra 1500

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2003 gmc pickup only have defroster only pulled the moter for the defrost off and it went one way then stopped and stayed there replaced the controller which has the switch in it and still had the same problem replaced the defrost motor and still have the same problem if I am right there is nothing else in the system any ideas I did pull off the pass side and check the wires there also

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  • norm doree Sep 29, 2010

    sorry but cant be this controller is all electronic there are no hoses at all just a black and a blue plug in the back of the unit



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Hi! The problem could be on the PCM (powertrain control module) itself. The PCM has connectivity on all electrical current that runs inside the car which includes the engine, transmission, accessories, etc. If the capacitor on the PCM is faulty something else fails. A good example will be your defroster. You will need to have the PCM replaced to resolve this. HOpe this helps and thank you for using FixYa!

Posted on Sep 30, 2010

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This is caused by a loss of engine vacuum to the dash controller, the vacuum comes from a vacuum reservoir under the hood then a line goes through the dash on the passengers side, make sure u have vacuum at the control head, at least 18 inches,when vacuum is lost to the control the default air flow position is the defrost vents for safety reasons, it is the only vacuum motor that is held on to turn the defrost off, that is to say it is normally open, all the rest of the system vacuum motors are normally closed

Posted on Sep 29, 2010


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