Randomletters
Member
- Joined
- Apr 12, 2011
- Location
- El Paso, TX
Check for an exhaust leak after the O2 sensor, but before the cat. When an exhaust leak forms, it not only blows out exhaust, it sucks in air on low pressure waves. This excess oxygen totally prevents the reduction end of the cat, and makes you fail for NOx, but it actually helps the oxidation end, so it will bring your HC down somewhat. The only thing is, when that is the case, it usually hurts more at low speed than at high. Still, it would be worth a look.
My girlfriend's Saab failed on NOx with everything else low, but NOx over 800. Found two exhaust leaks before the cat, just torqued the bolts down a bit and took it back in, and NOx dropped to under 30. But again, it was much worse on low speed.
My girlfriend's Saab failed on NOx with everything else low, but NOx over 800. Found two exhaust leaks before the cat, just torqued the bolts down a bit and took it back in, and NOx dropped to under 30. But again, it was much worse on low speed.