5
votes
3answers
32k views

Check Engine code P0420 Catalyst efficiency below threshold bank 1

After months of normal driving with no problems, my 2003 Honda Civic EX check engine light came on during a long trip. Got it scanned and it's P0420: Catalyst efficiency below threshold bank 1. They ...
10
votes
2answers
5k views

2005 Dodge Ram: easy way to diagnose code P0420?

My truck is reporting a code P0420, which apparently is "Catalyst System Efficiency Below Threshold (Bank 1)" which can either be the catalytic converter or the rear O2 sensor. The code came on at ...