× Auto Repair Pros Member Benefits TechHelp Knowledge Base Forums Resources My iATN Marketplace Chat Pricing About Us Join Industry Sponsors Video Members Only Repair Shops Auto Pro Careers Auto Pro Reviews
Join Now
International Automotive Technicians Network
Re: Isuzu NPR/NQR P0420
Posted to HD/Fleet Forum on 5/12/2018

check low side fuel pressure, should be 75-90 at idle and 170-195 wot. if it is not in this range replace both fuel filters and test again, if this doesn't fix it we need to know manual regen temps. Login to read more.