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Nissan expert
Nissan expert, ASE Certified Technician
Category: Nissan
Satisfied Customers: 10370
Experience:  30 yrs experience, ase certified, shop owner
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Nissan Xterra: code P0420 Bank 1 tw catalyst system

Customer Question

Have a Nissan Xterra. Get code P0420 Bank 1 tw catalyst system. I have been told different things. Do I need a converter or an O2 sensor ?
Submitted: 7 years ago.
Category: Nissan
Expert:  Nissan expert replied 7 years ago.

hi i can help you , the most common cause of this is the convertor , here is a couple of tests to do let me know what you find

Customer Concern:Check engine light is on. Trouble code P0420
Tests/Procedures:1. Watch the voltage of the front and rear O2 sensors. When cold, the front and rear voltage cross-counts should look the same. As the catalytic converter is lit, the rear O2 sensor voltage will start to decline to a small wave or a flat line voltage.

2. The temperature of the catalytic converter should be hotter on the outlet than the inlet. Do these checks after holding the RPM at 2,000 after a cold start.
Potential Causes:Catalytic Converter
Oxygen Sensor
Tech Tips:If the oxygen sensors are cross-counting and the fuel trims are normal, most likely fault will be a catalytic converter.

Nissan expert and 3 other Nissan Specialists are ready to help you
Customer: replied 7 years ago.
Not sure what you mean by cross-counts. Is that the voltage between the two ?
Expert:  Nissan expert replied 7 years ago.

cross count is a measure of the amount of times the sensors switch from lear to rich

unfortunatly 99 percent of the time it turns out to be a bad convertor anyway

Customer: replied 7 years ago.
Was not the convertor.
Expert:  Nissan expert replied 7 years ago.
how did the o2 sensors do on the test?