Quote:
Originally Posted by smug01
The secondary cats are required to keep the vehicle emissions in check while the diagnostic is run on the rear O2 sensor. This is required each drive cycle, where the ECU modifies the fuel air mixture into a region that makes the primary cats less effective in reducing emissions. I believe this revised diagnostic was implemented in 2010 regulations.
Once the diagnostic is complete, the primary cats are sufficient to meet emissions. Since this diagnostic will likely complete within the first few minutes of a drive cycle, you should have no problem passing a smog check, based on emissions measured.
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My understanding is there is no O2 sensor past the first set of cats.
