I have 2003 Maxima that will not pass smog in California. Error code that shows it is 02 censors we have changed them and the computer then drove it 100 miles now it is coming up 02 censors again? 02 censor’s volt readings are above normal. The latest smog test showed gross polluter EGR valve working correctly. This vehicle has been to 5 different shops and can’t find the problem can anyone help!

 

Not 100% sure.. Maybe the pre-cats are clogged.

 

All the O2 sensors were replaced? Which O2 codes are you getting?

S

 

Not sure took it to the garage they changed out the ones that they said were bad. They also check the 02 censors by directly bypassing the computer. The censor readings were normal but when you hook it up to the computer the reading are well above normal so we changed the computer now we are getting the same readings.

 

Has all the OBDII monitors completed the drive cycle? Post your failed ASM test results so we may help.

 

The O2 sensors just read the mixture, so if the sensors are new, and the readings are whacked, then the mixture is whacked.

 

So they were changed.. Codes reset and you drove 100miles and the O2 codes come up again?

 

It sounds like you need to replace your pre-cat or both pre-cats.

 

If the A/F O2 sensor voltage output is high as you say, then the exhaust oxygen content is low which indicates a rich mixture. A rich mixture consumes nearly all the oxygen. It could be excessive fuel pressure or the fuel injectors are leaking big time or extreme back pressure.

 

Sounds like it's precat time.

Or, you can move to a state that doesn't do sniff tests on our cars and say fck it.

 

These are the numbers for the NO (PPM) that failed. For 15mph meas at 2568 and for 25mph it meas at 2520.. anyone have any ideas????

 

Did you even read our responses?

 

Excessive Oxides of Nitrogen is caused by anything that makes combustion temperatures rise. The EGR system plays a big part in cooling combustion temperatures. Could be a plugged EGR passage, EGR valve failure, leaky EGR vacuum hose. Also an excessively Lean air/fuel mixture will cause elevated temperatures. Cooling system problems can also contribute to this issue.
If you ever ran the car for an extended time with bad coils generating misfires, then the CATS are probably gone. You never indicated if you are throwing any OBD fault codes. If there were fault codes why would the shop put it on the ASM test.

 

yes thats what happend

 

i dont know if this helps but the o2 censors read 1.275 as soon as you hook them up without the car running it slams the 02 censor right away

 

There is need to investigate all of the OBD fault codes as a first step to address your problem. List all the codes so we may help you.