Question

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

Answer 1

P0420 Catalyst system efficiency below threshold Bank 1

This is more of a catalytic converter that degraded, over time catalytic converters, does degrade.

On this VW the owner stated he replaced the catalytic converter for an emission test and just to pass the emission test a catalytic converter was installed. It also had an 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 performance of the PCV valve it also contributed to an erratic idle. An inspection of the ignition system was also performed.

 

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

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

Answer 2

P0420 VOLKSWAGEN - Catalyst System Efficiency Below Threshold Bank 1
Read more: https://www.autocodes.com/p0420_volkswagen.html