Q: My 2007 Nissan Titan had the SES light come on last week. I borrowed a friend's OBD scanner, and the resulting code was P0430. I cleared the code and it hasn't come back on. Could it have been a computer glitch that only happens once? I didn't do anything but clear the code.

A: It's never that easy, and the light will come back on. P0430 means the Bank 2 catalytic converter is below its efficiency threshold. This is determined by the air/fuel sensor mounted in the exhaust system before the cat, and an oxygen sensor located downstream. The powertrain control module (PCM) compares the oxygen content in the exhaust before and after the catalyst to determine if it's doing its job burning up harmful emissions. There are failures other than the catalyst that can produce this diagnostic trouble code, and there's a long, drawn-out diagnostic procedure to eliminate them all before replacing the cat. They include checking for exhaust leaks, intake leaks, bad plugs, injectors, or improper ignition timing -- not to mention inaccurate sensors and aftermarket add-ons. But from experience, if the engine runs well with no aftermarket tuning and no additional trouble codes, the majority of the time it is a simple failure of the catalytic converter. The PCM runs a catalyst Readiness Monitor to self-test the system before setting the trouble code. That's why your SES light is currently out. It can take days or even weeks before the monitor is complete, determines a duplication of the failure, and sets P0430 once again. An important thing to keep in mind is proper identification of the failed catalytic converter. Remember, your 5.6-liter V-8 has one for each bank of four cylinders. Bank 2 is the right side of the engine (passenger side). The converter is actually part of the exhaust manifold, and runs about $850 plus 3 or 4 hours labor to install.


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