on u-tube a couple guys show a much cheaper 14 dollars fix for this not easy but can be done im tj and have blogged on this before,the car may run ok but gas mileage and will not pass emissions where applicable have had this problem multiple times it is listed under engine and drive train also
Problems for specific Cadillac Seville STS years:
Car problem reports
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Newest reported 2003 Cadillac Seville STS problems
The torque converter clutch (TTC) may stop working due to an internal transmission failure. The Check Engine Light will illuminate if this occurs. Our technicians tell us the transmission will require dis-assembly to correct this concern.
A Loose or worn gas cap may cause Check Engine Light to illuminate.
An intake manifold vacuum leak can develop from a variety of sources, often causing illumination of the Check Engine Light with codes P0171 & P0174 stored. Thorough diagnoses will be necessary to pinpoint the cause in order to make the correct repairs. A "smoke" machine is often used to isolate the cause of difficult to find vacuum leaks.
One or more heater & AC (HVAC) temperature and/or air delivery mode door actuator may fail, resulting in improper temperature or air delivery. If this occurs, fault code(s) should be stored in the HVAC control module which should assist in diagnoses.
The trunk pull down switch may fail causing the trunk lid not to close completely. Our technicians tell us that the failed switch can be replaced without changing the complete pull down motor assembly.
One or both transmission output shaft seals may leak. Our technicians tell us that worn bushings inside the transmission could be the cause of the damaged seals. Our technicians tell us that if a bushing is worn, excess play will be noted where the drive axle attaches to the transmission.
The engine may develop an oil leak from the lower crankcase portion of the engine block. Our technicians tell us that the engine must be removed from the vehicle to properly repair this oil leak.
The anti-lock brake system (ABS) control module may fail causing the ABS light to illuminate. Failed modules should be replaced to restore ABS operation.