‘97 850na Wagon failed smog test

[SlowandSteady]

Greetings,

Just returned home from failing emissions test due to well beyond max NO measurements indicating the engine is running too lean. Ran into this same issue 2 years prior when I became the owner.
At that time I replaced the catalytic converter (as existing was not CARB compliant), both O2 sensors and subsequently passed with flying colors.
In the interim I have replaced the PCV system (6 months ago) in addition to standard preventative maintenance.
I will occasionally get a CEL that will show DTC for SAS, but otherwise she runs very well at just over 260,000 miles. Any advice or suggestions are appreciated by the knowledgeable folks who frequent this awesome site.

[erikv11]

Do you know if the O2 sensors were Bosch? If they are aftermarket, after two years it would not be surprising if one of them was bad already.

[abscate]

You’ve probably got some vacuum leaks making you run lean, which will max out the NOx

[SlowandSteady]

Both O2 sensors were replaced with Bosch (15097/15062). Strongly considering doing the same as that enabled the wagon to pass emissions 2 years ago. Any thoughts on the secondary air injection valve causing premature o2 sensor failure? Or is 2 years their typical life span?
In the meantime I will investigate vacuum leaks.
Thank you erikv11 and abscate!

[erikv11]

Any thoughts on the secondary air injection valve causing premature o2 sensor failure? Or is 2 years their typical life span?

SAS problems will not affect O2 sensor lifespan.
The Bosch units should last well over two year, I would expect them to be working fine.

[SlowandSteady]

Copy. Thanks again.
Not sure if it is relevant as I am not very savvy with the app (850 OBD2) as I have only previously used it to obtain accurate odometer reading and reset maintenance.
Yesterday I ran a scan utilizing the app and it is only showing “Bank 1 Sensor 1 present” in regard to o2 sensor location.

[abscate]

Can the app read fuel trims on that engine, anyone?

[jmartin919]

Aleksi can help you with the app: [email protected]
Email him directly.

[erikv11]

That's a front oxygen sensor code. This code is not usually indicating problems with the front sensor, though, Plus you just replaced it with a good Bosch unit (Although it wasn't from eBay right? Lots of Bosch counterfeits there, they have been called Genuine Rupert Busch" ). Fuel trim reads will help you pinpoint a vacuum leak issue. Note that SAS is hooked into the vacuum line system, a leak there can cause this code.

This code is usually caused by one of:
vacuum leak (extremely common)
>> inspect all vacuum hoses; consider just replacing them all because 30 year old rubber tends to crumble or turn to mush (viewtopic.php?t=65002)

exhaust manifold leak (common)
>> you need to closely inspect the manifold for cracks and listen for leaks; this is not easy to detect. Even a small crack in the flex pipe between the exhaust manifold and the catalytic converter

dirty or underperforming MAF sensor (uncommon)
>> first step is to clean it. you must use "MAF cleaner" or similar electronic parts cleaner. I used to think cleaning the MAF was useless but have become a bele=iever after finally having a couple actually, dirty MAF sensors on our cars. The air flow detection wire pretty much has to be visibly dirty to need cleaning. This is done by removing the MAF, visibly inspecting the wire. Never touch the sensor wire with anything except MAF cleaner.

[SlowandSteady]

I will be emailing Aleksi for insight regarding the app. I mentioned the “bank 1 sensor 1 present” message as I thought it odd that there was no mention of the 2nd (downstream) o2 sensor. Both sensors were purchased from my local auto parts store so hoping that they are not counterfeits.

I will definitely be taking a close look at all of the vacuum lines with zero hesitation thanks to the next level post/tutorial. In addition to inspecting for exhaust leak(s) and cleaning the MAF. Thanks again!