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Ask sprinkles08 Your Own Question
sprinkles08, ASE Certified Technician
Category: Jeep
Satisfied Customers: 22807
Experience:  Chrysler/Dodge/Jeep Master Certified, ASE Master and Advanced Certified, Trans and Hybrid Specialist
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Customer Question

Submitted: 9 months ago.
Category: Jeep
Customer: replied 9 months ago.
I also added a can of sea foam to a new tank of gas to hopefully loosen any deposits it may have
Expert:  david craig replied 9 months ago.

Hi Im David thanks for visiting the site. do a back pressure test to see if your cats are clogged.

Expert:  david craig replied 9 months ago.

checking in to see how its going

Expert:  david craig replied 9 months ago.

do you still need assistance?

Expert:  david craig replied 9 months ago.


Expert:  sprinkles08 replied 9 months ago.

Hello and welcome to JustAnswer!

P0420 is an efficiency failure of the catalytic converter and an be caused by a few things.

It could be an exhaust leak before the converter which is drawing air into the exhaust stream through venturi effect.

It could be a lazy upstream oxygen sensor. If the sensor is aged or the downstream sensor was replaced leaving an aged upstream in place then it can set a converter efficiency code.

The most likely cause would be the converter itself.