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.
Check Engine Light Due to Intake Manifold Vacuum Leaks on Cadillac Seville SLS
Average mileage: 111,600 (59,000–143,000)
18 people reported this problem
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intake boot cracked due to bad front motor mounts
Found a hose was not plugged in, plugged it back in. Error code went away in about 10 seconds.
P0101, P0300, P0131, P0171, P0174