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Steve, ASE L1 Master Technician
Category: Nissan
Satisfied Customers: 5494
Experience:  25+ Years experience as a professional working automotive technician; ASE L1 master technician
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I have a 2004 nissan xterra and the service engine soon light

Resolved Question:

I have a 2004 nissan xterra and the service engine soon light is on. The codes are p0430 Catalyst system efficiency below threshold (bank 2) and p0328 Knock sensor 1 Circuit High Input (bank 1 or single sensor) (3). IT did not pass emissions testing and I just had a tune up done and new air filter and oil change.
Submitted: 7 years ago.
Category: Nissan
Expert:  Steve replied 7 years ago.
   The P0420 code means that the computer has determined that the catalytic converter on the passenger side of the engine is not operating correctly.   It does this by measuring the amount of oxygen in the exhaust both entering and leaving teh converter.   A normally operating converter will use up almost all of the oxygen as it passes through; if it does not the computer concludes that it is not working.     
   This code can be caused by an exhaust leak in between the converter and the engine; check carefully for a broken or leaking exhaust manifold or exhaust manifold gasket on the passenger side of the engine. broken exhaust studs are very common on this model.    If there are no exhaust leaks that could allow air into the exhaust system, then the converter has likely failed and will need to be replaced.
   If the CAT is faulty, you may want to call your local Nissan dealer service department with your VIN number and mileage; there is a federal warranty on converters for as long as 8 years on some models. If yours is still within federal warranty they will replae it for free even though the manufacturer's basic warranty on the vehicle has expired.
   The knock sensor code can be caused by a faulty knock sensor, an internal computer fault, or by a problem with the electrical circuit in between the knock sensor and the computer.    usually replacing the knock sensor resolves this issue.
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