kbeen
SDD Junior Member
On my 09, 6.4 L I get the PO420 fault code. which is Catalyst System Efficiency Below Threshold (Bank 1). I know you have the 3 exhaust temp. sensors in the piping. has anyone already been down this road and knows which one of the three can cause this code. That is if it is not the Cat. itself. thanks for any input. 
