I just moved to Northern VA and for the first time I have to pass emissions! Problem is I keep pulling codes. Details. 3.0 with 00vi and all emissions hooked up. budget y-pipe, Cattman cat, and Cattman 3" Cat back.

I was originally pulling these two codes: 0304, 0503. The Knock sensor was actually was bad....so I cleared out the 0304 code after replacing the KS (btw...you will know if your KS is bad...your car runs like s#$t). I figured the car has 205k on it....probably time to change the o2 sensors. So I replaced both the sensors in the y-pipe. But now for the first time EVER I just pulled an 0702 code!!!

After reading 20 threads with people complaining about having this code Im not really sure how to remedy it. I am guessing that because I dont have the stock y-pipe with the cats it is making the ECU nuts.... Will this go away with time or a couple of hundred miles? Thanks in advance and dont kill me if this has been covered (sorry in advance) My entire exhaust system is new and so are all of the sensors (except the rear 02)

NOTE: I also pulled an EGR code 0305 but I believe I remedied this already. When I put the 00vi back on after replacing the KS one of the vacuum hoses was dry rotted and split and I didnt catch it.

 

Oh....since replacing the Knock sensor the actual CEL light has not come on. I am getting this information by manually checking the codes. No need to take my car to a shop and pay them $38 to tell me I have a Code and they just failed me for emissions. :/

 

I have an aftermarket Y-pipe and have no problem passing emissions. That code you listed, 0702, is for the catalytic converter. I noticed you have an aftermarket cat. I've read people have problems with them concerning emissions. The rear O2 sensor monitors the function of the cat, so maybe it could be bad.

 

I would replace the after cat 02 sensor, and get the 12mm O2 spacer. Contact 02spacer.com (sales@o2spacer.com) tell them you want the 12mm one that is not listed. this solved my problem last month. $ 25 shipped.

I didnt have a cat code until one of my O2 sensors went bad at 222K. After I replaced all three, got the code for the first time with my Y pipe and magnaflow cat.

 

What does the 12mm spacer do? Thanks for the heads up.
edit: Answered my own question by reading

From o2spacer.com:
O2 Sensor Spacer - CEL / MIL Fix - O2 Simulator

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Takes less than 10 minutes to install this O2 Simulator!

Do you have a 1996 to Present vehicle with CEL, ECU or MIL Light on and have a test pipe, high flow cat, downpipe, or high performance exhaust installed? Then our O2 Simulator is perfect for you!

How our O2 Simulator works is it removes the troublesome O2 sensor from direct exhaust flow. 99.9% of the time this tends to be the rear most O2 sensor in modified exhaust systems (at or after the cat). This sensor is also known as the 'Heated Sensor Circuit' or 'Bank 1 sensor 2'. With a modified exhaust system, this sensor will receive higher temperature and a higher flow rate than stock. Thus causing the ECU to read that the exhaust system is out of balance. When the ECU sees that the system is out of balance it will throw a code and drop into 'limp mode'.

When you add our O2 Simulator it will remove the troublesome O2 sensor from direct exhaust flow and provide the ECU the expected exhaust balance. Thus allowing your ECU to run the motor optimally.

Our O2 Simulator simply is screwed on to your existing O2 sensor and the assembly is replaced into the O2 bung.

This is an easy & inexpensive fix that will ensure the O2 sensor is not overloaded by your added exhaust flow. Easier to install and more reliable than an electrical device! No soldering or splicing involved !

O2 Simulator/Spacer FAQ

 

run a tank of Chevron techron...then report your results. I bet the car jus needs to adjdust to the new O2s.

 

What size is the bung in a 97 maxima (bung is behind the cat). I was able to confirm that the bung size in a 95-96 is 12m because the oxygen sensor is in the cat itself. But advanced auto has the rear sensor on a 97 listed as 18m threads....

 

I will try this and let you know.

 

The 96 is definitely 12 mm. I dont know about the 97. The threads you find on making on from spark plug spacers are all 18mm. Go to the parts store and get an 18MM anti-foul adapter and see if it is 18mm.

 

I hate emissions too, I have had to retest everytime I had to go. I am concerned about you clearing the codes because when you do that and retest when they hook up to the obd some systems may read not ready, then they may say you have to do the roller test. If you do the roller test it may not pass because of the aftermarket cat. If you clear all the codes you may have to drive it around a couple weeks (if you have that much grace period) in different ways or follow the drive logic deal that is posted somewhere here on the forums.

 

I learned that the hard way. Thought I was being slick and reset it 5 minutes before I went for a test. lol yeah Im driving it around for a week or so in hopes that the ECU learns my exhaust system.

 

EC-40 in the 1997 FSM goes over the "System Readiness Test". There is a procedure that outlines the driving pattern necessary to complete all of the SRTs.

 

And driving that pattern would either get you arrested or killed in most states!

The one that is hard to set is the CAT. The others seem to set within 1 or 2 days of city driving. To set the CAT on mine, I figured out I could drive for about 30 miles at 70, then about 10 at 55, only by accident as it was a trip I make a lot.

 

Passed emissions! It took the ECU a couple of days to get used to the readings from the front o2 sensors. I did order the rear o2 sensor spacer but have not installed it. If my CEL comes back on I will update the thread and post results after the spacer. As of now Im going to run it without the spacer.

 

Congrats, you are safe for another 2 years probably.

 

Congrats on passing emissions! Like you stated earlier I have an aftermarket y-pipe with a magnaflow CAT also. I got the 0702 yesterday. I get it about once a month when doing a cold start.

My inspection is in October so for the last 2 weeks in September I'll be warming her up for at least 10min before every drive. I know one of the mechanics at this shop so I'll ask him to let it idle for 15min in the parking lot before inspecting it.