Check Engine Light Due to Loose or Worn Gas Cap on Cadillac STS

Problem Description and Possible Solution

A loose or worn gas cap could be cause the Check Engine Light to illuminate.

Problem Data
RepairPal Verified
Average mileage: 86,375 (28,000–145,000)
6 model years affected: 2005, 2006, 2007, 2008, more2009, 2010
22 people reported this problem
Viewing 1 - 4 of 4 comments
STS V8, "check engine light" comes on occasionally, dealer states no trouble codes are evident, has no idea how to repair, GM will give no assistance, after creating a complaint file on it.
Last seven months the check enine light keeps coming on. dealer shows no interest in repair or trouble shooting.
Rough idle and about 55 to 60 mph rough ride
That smooth out about 70mph could this be the evop purg pump