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