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2004 Titan LE throws 420 and 430 codes

845 Views 3 Replies 2 Participants Last post by  FishnAlaska
My daughters 2004 Titan with 240k miles, runs great and always has. Oil changed regularly. Check engine light came on right before yearly inspection time. ( emissions state). Shows codes 420 and 430. Put in new post cat O2 sensors both side, mass air flow sensors, new plugs and oil change, no exhaust leaks. Tried the O2 sensor extenders, still shows code. I can drive 160 miles at highway speeds and no codes. When I drive in town maybe 10 miles or less, codes come up. Can't get yearly tags until it passes inspection. (Texas). Real time info shows everything is ok. What am I missing?
Don't want to take it to someone that will just throw parts at it-like I did. Thanks.
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That's what I'm afraid of. Anyway to tell for sure? Is there anything you can ad to the fuel to clear them up? I just need to get by the emission to get it tagged, then I can drive it while working on it.
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