We have an 08 Equinox Sport that is throwing the P0420 Catalyst System Efficiency Below Threshold (Bank 1) code. The dealer we got it from agreed to fix the problem as part of the deal since the code was on when we test drove it. Well after a FULL DAY in the shop with them replacing the bank 1 cat they said it was fixed...... but after driving it less than 35 miles the CEL came back on with the same code. :angryfire: :angryfire: Could it be the 02 sensor? Hard to believe that a brand new $600+ cat would also be bad. The vehicle has only 118K miles and in very good shape. The BIGGEST problem is that the STUPID factory auto start will NOT work when the CEL is on! What GM rocket scientist came up with that idea? Any info or help would be greatly appreciated.