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Jay, Nissan Technician
Category: Nissan
Satisfied Customers: 19627
Experience:  20+yrs experience with Nissan & Infiniti Trained & Certified.Currently still working for Dealer
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My 2002 pathfinder faile emission test. the test information

Customer Question

my 2002 pathfinder faile emission test . the test information revealed 1)PO420 catalyst system efficiency below threshold bank 1. 2) P1491 manufacturer specific code.
How can I fix this.
Submitted: 1 year ago.
Category: Nissan
Expert:  Ron replied 1 year ago.

Hello and thank you for your question,

The code P0420 sets in most cases due t a failing Catalytic converter on bank one, the most common cause for the P1491 to set in most cases is caused by a failed Vacuum Cut Bypass Valve. The fix usually requires replacing the bank one converter as well as the cut valve located under the truck near the spar tire. I have enclosed the location in the link below. Copy and paste the link to your browser to open and view it. Post back if you have more questions and or need more help and we can work from there.

Expert:  Jay replied 1 year ago.

Hello my name is ***** ***** thank you for your question.

Let me give you a little more details on your codes you provided.

1.) The P0420 is for Bank 1 Catt Converter. Bank 1 is the Passenger side of the engine. The way this code is generated is when the rear 02 sensor starts to mimic readings of the front 02 sensor. The Catt Converter is between those two sensors and if functioning properly the rear 02 sensor should never mimic the front 02 sensor. When it does mimic the front 02 sensor, that is what generates a catt converter code. Nissan uses Platinum to converter exhaust gases. This is why the Nissan part is allot of money. You can get the part much cheaper buying it after market, but a majority of the after market catt converters don't use Platinum to converter the exhaust gases. Because of this, the material used may not convert the gases to the vehicle specification which could result in a Catt Code to return even with a new catt converter. So I recommend you get the part from the dealer.

2.) The P1491 is for the Vacuum Cut Valve. This is a Plastic valve in the back of the truck that is part of the Evap system. The most common cause is indeed valve failure. Most of the time caused by when the tail pipe flange rusts away and the heat of the exhaust gases when the pipe is broken points right at this valve. There is a solenoid also that goes to the valve. The heat of the exhaust gases causes the valve to melts. So that is the most common thing found to cause this valve to fail. Here is a better picture of the valve for you along with the solenoid and another image of the parts location for you.

Let me know if you have any more questions on this.

Thanks Jay!