My check engine light came on so I checked the codes and it was an 0409(po133).I replaced the sensor with a denso direct fit sensor and all was good for about 2 months.Check engine light just came on again and it is the same code.There are no other codes.All stock except i did do the resistor mod for the knock sensor.Any ideas?

 

I'm having the same issues just replaced all threee o2 sensors and was getting the same code then someone pointed out to check my fuses (DUH) so i will start there i suggest you do the same

 

He would be getting codes for all O2 sensors if the fuse was blown. It's either a defective 'NEW' sensor or a short in the wiring to it.

 

I had the same issue trying to pass the damn emissions. My mechanic told me to drive around on the highway and local for a total of 50-60 miles after replacing the 02 Sensor. It actually worked.

 

I reset the computer after changing the sensor and the light stayed out for a few months and just came back on.Maybe a defective sensor or maybe something else is causing the sensor to fail.I may try another o2 but if it happens again i'm out 2 o2 sensors which would tick me off.That's why I'm trying to figure out what else may cause this problem.Thank's for all your help.

 

I've been having this same issue for months, seems to be getting more common amongst the 4g's. I'm looking into an o2 sim .... might work.

 

have you tried hooking up a multimeter, or an obd2 scanner that can read o2 voltages? It helps alot. when you hit the gas the voltage should change quickly.

 

take the O2 sensors back out and check for carbon fouling. if you're running rich you'll f up you're O2 sensors. check your plugs for carbon too. carbon fouling may be due to leaky injectors.

do you put any fuel addtitives in your tank? that could also screw things up.

 

I did not use any fuel additives since I installed the new o2 sensor.I will check the o2 sensor for carbon build up.Is there any way to clean an o2 sensor?I will also check the plugs to see if it looks like it is running rich.Thanks for the tip.Any other signs of a leaking injector?

 

I pulled the o2 out and it looked good with no carbon build up. I will pull the plugs for that bank and see how they look.I'll keep you all posted.

 

Finally pulled the plugs and if anything look a little on the lean side but all looked the same and looked good. I think i'm going to spray electric contact cleaner in the electrical connector (car side) because the light went out today but i'm sure it will come back on.

 

cheap gas maybe... 4th gens needs 91 or better and also check o2 sensor fuses. other fuel mixture problems can cause o2 sensor code but not necessary meaning your o2 is bad. Try some simple fix first like spending the cash for premium at least two tank fulls, Clean throttle body, MAF new filter etc... specially if you've just change and o2 and you're getting code again and again. Not o2 it something else.

 

I always use 93 octane.I also cleaned the maf,throttlebody,and installed plugs,air filter and fuel filter in the last 5000 miles.

 

my suggestion now would be to install a knock sensor... You've stated that you have a resistor install for several months and those are good and all but if you have pinging the resistor won't be good for your engine.