P0420 pops up after Header kit install
 

I just had the longtube header kit from stainless works put on today. I thought all things were great until i took it out tonight and noticed it was making a weird sound. sounded like either water or air being pushed out at a rapid speed, couldnt tell if it was just me or if something was wrong like a leak somewhere(place were i had the install done was already closed). I just went to go workout and then got back in the truck and started it up and noticed the engine light was on. got my xcal 3 out and ran DTC check and it popped up P0420 and in the description it said something about the CATS. might this be something about the sound i was hearing or is this because im running the truck stock(custom tunes wont be in till sometime next week hopefully).

Thanks,

Could be one of the possible causes in bold, probably not anything in grey.

P0420,"Catalyst System Efficiency Below Threshold (Bank 1).
--Possible Causes--
- Use of leaded fuel
- Spark timing retarded below spec
- Oil contamination
- Cylinder misfiring
- Damaged HO2S
- Damaged ECT senor
- Downstream HO2S wires improperly connected
- Fuel pressure too high
- Damaged exhaust system pipe
- Damaged exhaust manifold
- Damaged muffler/tailpipe assembly
- Damaged catalytic converter
Note: The Powertrain Control Module(PCM) tests the catalyst efficiency by monitoring the rear Heated Oxygen Sensor. The Diagnostic Trouble Code(DTC) is set when the catalyst efficiency is below an acceptable level."


Check and make sure all of your sensors are intact by rolling under and following the tailpipe up to the engine.

well i got under the truck today and noticed that it wasnt welded around the cats. they are just clamped to the exhaust pipe. i think thats the problem. im getting it looked at sat. morning.

Before or after the cats? Anything past the last sensor doesn't matter. If it is before you have to have a real leak. Many exhaust systems clamp together before anyways I think.

are they original or aftermarket cats? some aftermarket cat aren't as efficient as OE. (fyi: i have no cats at all and periodically have the same code even with my rear HO2S turned off by bill:shrug:)

they are the hi flow cats that come with the header kit. So do you think this can be helped by tuning. The funny thing is i still hear the sound but the light isnt on anymore.

You need a retune after just LT headers or highflow cats. You definitely need one after both.

I'm running the truck stock right now. But the new customs are on their way.

Ok, I guess just be very nice to the pedal until you get the new tunes.

They said the found a small whole around the muffler and they welded that up. But the main problem is just the way the headers are made. They had the truck lifted and you could hear it while it was idleing, but where you could hear it, there isnt any wholes. So i guess its just something im going to have to live with but if you have the radio on, you really cant hear it.

little to late for being easy on the pedal:cheesy smile:. but ill keep that in mind PHP said they should be ready sometime next week.