So my truck has been throwing code 21 for quite sometime now. However I have replaced the o2 sensor within the past 5k miles. Could the new sensor be bad or possibly replacing the map sensor fix this. Truck doesn't run rough just smells like it runs pure alot and now that I've been working would like to fix it for the possible increase in mpgs.

Also drilled two holes into my air breather tube cover behind the grill with a two inch hole saw and put some sculpter wire mesh infront of it as I have read that some people take the cover off completely but I want to keep leaves and bugs out of my air filter. Thought I'd add that to those who think of this as I figured it to be a good idea.

Thanks for imput.

 

If a new oxygen sensor didn't fix it, it is very possible the wiring is damaged. Get a meter and check the continuity of every wire to and from the PCM to the oxygen sensor.