My oil also has gaa smell. I just replaced down stream and upstream o2 sensors now im getting p0172(system too rich)p0420 catylyst sytem inefficient bank 1 p2271 o2 sensor signal stuck rich) bank 1, sensor 2. 2011 regal 2.0. Is it my fuel pump?
The direct injection high pressure fuel pump would allow gas to leak into the crankcase on your vintage of GM vehicle.
And that will cause all those codes.
Tester
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