My cousin contacted me and asked me about a p0420 code that he is getting on his truck. I read around and found that it could be a bad cat, a bad O2 sensor, a bad engine temp sensor, or a bad fuel pump. He tested the pump today and found the pressure to be 60psi while running, 52 psi when shut off, 44 psi 5 minutes after shut off, and 40 psi 10 minutes after shutoff. So, my question is, does this indicate a bad fuel regulator? Would a bad regulator cause the truck to run lean and therefor throw the code? or is basically a bad cat with that code? I also have a freeze frame from his scan tool that he sent me. Any ideas guys? He cleared the code and it came back a week later.

DTC that caused the freeze frame PO420


Throttle position 14.9%


Engine RPM 546


Load value 2.3%


Air flow rate 6.89 GR/SEC


MAP sensor 39KPA


Coolant temp 201 F


Short term fuel trim 1 3.1%


Long term fuel trim 1 -4.6%


Short term fuel trim 2 0.7%


Long term fuel trim2 -4.9%


Short term fuel trim 3 40.6%


Long term fuel trim 3 99.2%


Long term fuel trim 4 83.5%


Short term fuel trim 4 65.6%


Vehicle speed 0MPH


Fuel system 1 Open 1


Fuel system 2 Open 1








I/M Monitors


Misfire Mon ok


Fuel sys mon ok


Comp comp ok


Catalyst mon oj


HTD catalyst n/a


EVAP sys mon inc


SEC air sys n/a


a/c refrig mon n/a


oxy sensor mon ok


oxy sen HTR ok


EGR system mon n/a