Hey folks, my check engine light has been on for a couple of months, and I keep getting the P0420 code. This is on my 2005 F150 with the 4.6L engine and about 150k miles. I’ve done a bit of reading, and it seems like it could be the catalytic converter, the O2 sensors, or maybe something to do with my fuel system. The previous owner swapped the stock exhaust for a dual Flowmaster setup, and lately, I’m also noticing worse gas mileage. I’ve already replaced the fuel filter. Should I try replacing the O2 sensors next, or take it to a mechanic to check the cat? Any advice would be awesome!
Before swapping out the O2 sensors, you might want to have an exhaust shop check if the catalytic converter is plugged. At this mileage, it could be the cat itself.
Farrell said:
Before swapping out the O2 sensors, you might want to have an exhaust shop check if the catalytic converter is plugged. At this mileage, it could be the cat itself.
Thanks! Do you think hitting it with a mallet to check for rattling would give me any clues?
@Steele
Yep, that could help. If you hear a rattling, it’s probably gone bad. Might still be worth a scan to check O2 sensor readings too.
I just got the same code after leaving the dealership last week. I’m planning to change the plugs, fuel filter, and maybe the O2 sensors to see if that helps.
Eden said:
I just got the same code after leaving the dealership last week. I’m planning to change the plugs, fuel filter, and maybe the O2 sensors to see if that helps.
If it’s an exhaust leak or plugged cat causing the code, fixing those first might save you from buying unnecessary parts.
@Farrell
True, plugs were on my list anyway since idle’s been a little rough. Might be time for an exhaust check too.
Does anyone know where I can grab those Motorcraft fuel filters for $5? That’s a steal!
Keegan said:
Does anyone know where I can grab those Motorcraft fuel filters for $5? That’s a steal!
Amazon, but look under ‘used’ filters with damaged packaging. They’re new, just come in banged-up boxes.
@Eden
Sweet, I’ll check it out. Any chance they come with free shipping?
Keegan said:
@Eden
Sweet, I’ll check it out. Any chance they come with free shipping?
Yep, if you’re a Prime member. Otherwise, it’s free on orders over $35.
P0420 could be an exhaust leak too. Even a small one can trigger that code. Check for any abnormal sounds at idle.
Kirby said:
P0420 could be an exhaust leak too. Even a small one can trigger that code. Check for any abnormal sounds at idle.
Thanks, I did notice a bit of a weird sound at cold start. Could be a leak, I’ll look into it.
Kind of late to the party here, but what ended up being the main issue with your P0420 code? I’m dealing with the same thing on my truck.
Dane said:
Kind of late to the party here, but what ended up being the main issue with your P0420 code? I’m dealing with the same thing on my truck.
Still figuring it out, but I’ll probably start with checking for exhaust leaks and maybe get the cat looked at.