Code P0420
10

Asked by Alfredo Feb 18, 2019 at 12:03 PM about the 2003 GMC Sonoma SLS Ext Cab SB

Question type: Maintenance & Repair

After replacing catalyst converter check
engine light lit. Scanner shows code P0420.
Changed both sensor but still showing code.
Any idea?

2 Answers
42,415

Auto_Centric answered 5 years ago

Check the engine fuel trim numbers ST and LT with a proper scan tool it's not difficult to read these numbers... improper fueling or a leaking exhaust manifold or pipe can cause P0420

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