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Unread 03-31-2014, 04:01 AM   #1
loose_electron's Avatar
Join Date: Oct 2011
Location: Guam
Posts: 259
Thumbs up Understanding and diagnosing Toyota P0420 DTC

I found an informative article on the PO420 Diagnostic Trouble Codes (DTC) and thought it was worth sharing since many of us fall under the category of exhaust leaks or may in the future. This was also my first chance to use my Scangauge 2 to diagnoise a code. The following are some highlights from the article.

- P0420 equals changing the catalytic converter, right? Not always.

- Your approach to diagnosing a P0420 should be in reality fixing bad MAFs, Exhaust Leaks, ignition coils, vacuum leaks, and other conditions that create extreme fuel trim conditions that degrade catalytic converters

- Check TSB's

- Check for exhaust leaks. This is important to do in order to make sure that nothing is throwing off the oxygen sensors, especially the rear O2 sensor. Fix these before condemning the catalytic converter.

- Test the rear O2 sensor

'04 Sport V8 4x4, 265/70/17 BFG MT KM2 E, HD Series TR beadlocks 17x8.5 +4" bs, NO Swaybars, TC+2 Long Travel, Spindel Gussets, Upper Coil Tower Gussets, LCA Cam Tabs, ICON frt CO 650lb springs w/resi, ICON Bypass w/Resi. Metal Tech(MT) LT Progressive Spring, MT specs-ICON developed LT shock-2.5 rear w/resi. Rear ARB, sPod, Shrockworks Skids
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Unread 03-31-2014, 10:01 AM   #2
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Join Date: Mar 2011
Location: Bend, OR
Posts: 700

This is a good article! I'll have to add the link to my Sticky on

Which I also should transfer onto this forum as well one of these days...
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