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2002 Volkswagen Jetta 2.0L with engine code P0420 how can be fix?

Vehicle: 2002 Volkswagen Jetta 2.0L

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P0420 Catalyst system efficiency below threshold Bank 1

This is more of a catalytic convertor that degraded, over time catalytic convertor do degrade.


On this VW the owner stated he replace the catalytic convertor for a emission test and just to pass the emission test a catalytic convertor was installed. It also had a erratic idle. Code where check and there was none, on a scan tool data the fuel trim was adding fuel , it was not even close enough to trigger a CK ENG LT.  But not even 25,000 miles there is a P0420.Inspecting the vehicle what was found that set a P0420 was a broken dipstick, Having a broken dipstick affects the perfomance of the PCV valve it also contributed to a erratic idle. A inspection for the ignition system was also performed.


 Inspecting when a tune up was perfomed revealed worn sparkplugs, Worn sparkplug can and do contribute a P0420, worn sparkplug will lean out the system and it does not have to cause the CK ENG LT to appear. It only show on fuel trim data.

The fix for a false P0420 was replace the dipstick, replace the sparkplugs the fuel trim returned to normal, and erratic idle condition was fix with it.

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P0420 VOLKSWAGEN - Catalyst System Efficiency Below Threshold Bank 1

Read more: https://www.autocodes.com/p0420_volkswagen.html

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