Q: Car won't pass smog.

What you do next depends on what particular part of the smog test your car failed. The car is tested for HC, CO and NOx levels. Different problems will raise the levels of different pollutants. If your car failed the NOx levels, that could be a problem in the catalyst or the fuel control system running lean. Both of those issues would produce a Check Engine Light with codes.

If the CO level was too high, that could also be a catalyst or a fuel system problem, with the system running too rich. That also would likely turn on your Check Engine Light. High HC might mean you have engine problems that will require major repair. It could be from a misfire, or it could come from excessive oil consumption. With the mileage on your car I could see that happening.

If the car is barely failing the HC level, you might be able to just squeak by by changing the oil. Sometimes old oil in an old engine will be diluted with fuel from old issues and cause the HC levels to rise. But if the HC level is high enough to fail, it’s a temporary treatment at best.

Solving emission problems can be a complicated subject, Here’s an article that gives a few tips toward coaxing a stubborn car through the emissions test. If that doesn’t do the trick, I recommend you have a certified technician, like one from YourMechanic, come and look at your car over and make any recommendations.