2003 Pathfinder failed CA smog, how can I lower NOX?

[alan19]

Failed 15mph NOX only. All other emissions pass.

They supposedly checked everything (EGR etc) and are recommending two new cats for $2400.

I'm trying to figure out if there's another way to get this car to pass. Any ideas? My understanding is this is generally due to engine running hot (lean)

No other emission test failures.

Speed......RPM.......%CO2......%O2......HCppm.....CO%......NOppm
15mph.....1778.......15.0.......0.02.........6.......0.13......569 (FAIL)
25mph.....1802.......14.9.......0.01.........5.......0.13......539 (Pass)

Max NOX@15mph = 494

Thanks for any suggestions
-Alan

[fueler]

cars usually pass smog BETTER when they are hot... cold cats dont work good. I always make sure my QX is nice and hot when im smogging it.

$2400 for cats is dumb.... look at it this way, "smog hookup" is $300 on average... with smog checks being every other year, it would take you 16 years of doing ghetto smog checks before you reach $2400.

My Q has never failed smog, and thats a miracle considering all the stuff ive done (overheated it to the red probably over 100 times)... driven it 50 miles with no coolant at all, etc etc etc

[Towncivilian]

Yeah, two cats don't cost nearly that much even with OEM parts.

Change the fuel filter, run a bottle of 20oz. Chevron Techron in a full tank of gas, clean the throttle body, and ensure the air filter is not excessively dirty and its seal is good.

[pelinors714]

to lower my NOx in my MR2 spyder i replaced all the oxygen sensors and the main catylic converter. everything went down A LOT from 18xx to 300 NOx

[Towncivilian]

You shouldn't have needed to replace the rear oxygen sensors, they just make sure the cats are actually working. If they are not triggering a CEL, don't bother replacing downstream sensors. In fact, I wouldn't even bother replacing upstream sensors unless they threw codes. Maybe on an ODB-I vehicle, but not on an ODB-II vehicle.

[alan19]

Thanks for the advice everybody. Car passed smog yesterday. Bottle of Techron + took the car to a "test only, pass or don't pay" check station.

Figured their interests are better aligned with mine, i.e. getting the car to pass. (as opposed to the check and repair place where the guy wanted to charge me $2400 for new cats)

[carnal_c30]

I just passed in my 2001 QX4,

for high NOX usually I hear clean EGR and also run a bit cooler- when the car is running hot NOX is usually higher

Glad it got taken care of!