http://www.thedieselstop.com/faq/9497faq/tsb/tsb/files/010907.pdf
see this site and look under article no.01-9-7 page 9
states reason for 0420 and 0430:
malfunctioning ect/cht
high fuel pressure
damaged exhaust manifold
cylinder misfiring
ho2's wiring concerns(shortened or chafed,bent pins)
damaged exhaust pipe/muffler/tailpipe assembly
retarded spark timing
