Why Do I still have a CEL after installing 02 Bung Extenders?

SonicVQ

Your rear O2 sensors need to switch between ~0.9 volts and ~0.1 volts to keep the ECU happy. If they are constantly at 0.28 - 0.29 volts they are too lean and the ECU will turn on the CEL.

Since the rear O2 sensors are now out of the exhaust stream from the extender/anti-foulers they don't "see" much of the actual exhaust and just the air inside the extender/anti-foulers. Air (or more accurately, oxygen) = lean.

On the newer VHR ECUs (2012+ ?) it uses the rear O2 sensor to check for an Air/Fuel sensor lean bias.

Here is a good video on what the ECU is expecting to see. If you know what it requires, maybe you can figure out a way to make the ECU happy.



I think most just get a tune and turn off the CEL or put back the cats.