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Threw P0420 after installing RalliSport UEL


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I've had the Rallisport UEL headers on my car for around a month now (it's awesome :lol:) and i haven't had any problems with it during that time. During this time, I only drove in the city with frequent stops and usually short trips around 15-20 minutes at a time.

 

Yesterday however, I was on the freeway for around a 20-30 minute trip and i got a constant check engine and constant traction control off and a flashing cruise control light around halfway to my destination. Upon returning home i pulled the codes and it reveals a P0420 code. I have just cleared the codes for now to get rid of the distracting flashing lights.

 

So I've searched a lot and come up with a few possible solutions:

-Heatproof paint

-header wrap

-finding tuner to flash it away permanently

 

So if any of you guys have dealt with this situation before and found a good solution i'd appreciate any help you guys can offer or suggest to me!

 

I have a 2009 2.5i PZEV btw.

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i read that it happens more often in colder weather since the header loses heat more quickly, but it isnt even relatively that cold in california compared to other places. I wont be needing to use the freeway again for the next couple of days but i remember reading that the reason the P0420 code initially pops up while on the freeway is because the ECU runs the check only after the engine is held at a constant load for a certain amount of time
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ECU runs the O2 check above 3/4 and below 1/4 a tank fuel and after 5 miles constant load above operating temp. The cold will cause the P0420, Mike (RalliSport) knows this but it isn't a persistent thing. Wrapping, and ceramic coating help the best way is to address it during the tuning process.
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Thanks gee-otto, i remember reading the same thing from you in a couple other posts :)

 

A quick update:

After clearing the codes on Saturday night, the car sat till Monday. Upon starting the car up Monday morning to go to work, it took quite a few cranks before the car turned on which was a bit peculiar. The car ran pretty crappily during the 10 minute drive to work (wanting to stall coming to a stop at redlights, hesitating when stepping on the gas).

 

When starting the car to go home later that day, it started right up like normal again and I ran a couple errands before going home with the car running perfectly normal again (no more hesitation/wanting to stall at redlights).

 

The car also worked perfectly today as well. An interesting thing I noted was it being much easier to get a high MPG reading on the little clock readout thing. I usually drive with it on to try to keep my foot from getting too heavy around town. It may just be a coincidence, but it is a lot easier to keep at a high reading now after the car settled back into proper working order from Monday morning.

 

I won't be going anywhere for 5 miles at a constant load till the weekend and my tank is also around half full so I'm going to assume the P0420 won't pop up again this week.

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update:

so i was on the freeway today going to the same place i went to last week when the CEL popped up. gas level at just a bit over the last 1/4 of the tank so i was assuming the O2 check wouldn't be run. made the trip without a hitch and no CEL.

 

so on the freeway on the way back the gas level was now at the last 1/4 of the tank and halfway to my destination the CEL came on along with the traction control light and the blinking cruise light just like last week. today was a relatively warm day at 70F so i dont think temperature would be the cause of this.

 

ive been monitoring the front o2 sensor every now and then this week via the torque app on android and everything seems to be okay with that, voltage reading fluctuates back and forth between around .2-.8ish which is normal from what i remember reading.

 

also fueled up and calculated mpg which is back up to a more normalish 19ish mpg for 90% city and 10% freeway miles. i was probably subconsciously gassing it around a bit more last fill up after i installed the headers and got a dismal 15mpg

 

so anyways, any suggestions on how to narrow down my problem some more to figure out where it actually stems from?

-front o2 seems to be working fine(still figuring out how to monitor rear o2 on torque app)

-mileage seems normal based on the one full tank ive run while having the headers installed

 

sidenote: ive been hearing a sort of ticking noise from the right side of the car when it is in its warmup routine which goes away when the car is warmed up. however i also hear it if i am gassing and have the passenger window down and pass by a wall or another car which gives the sound something to bounce back into the car with. could that be an exhaust leak or just something normal that i've never noticed before and made more prominent with the headers?

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Could also change out both upstream and downstream O2 sensors while your at it with the heat wrapping or what not. I live in NJ and my CEL came on during the Polar Vortex, went out but comes back on every now and then if snow or a puddle comes in contact with the catalytic converter. However, 11 months out of the year before the cold hit no codes. Not worried much about it, threw my stock EL on and the code is gone, I'll wait for the warmer months and throw the UEL back on.
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Mine used to come on @ 3/4 and sometimes at 1/4 tank as GEE-OTTO said. After a while it just stopped coming on... I don't know if the fact that you're PZEV makes computer verry angry, but for me it stopped being an issue after a month or 2.
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Could also change out both upstream and downstream O2 sensors while your at it with the heat wrapping or what not. I live in NJ and my CEL came on during the Polar Vortex, went out but comes back on every now and then if snow or a puddle comes in contact with the catalytic converter. However, 11 months out of the year before the cold hit no codes. Not worried much about it, threw my stock EL on and the code is gone, I'll wait for the warmer months and throw the UEL back on.

 

It's not even anywhere near as cold in California as it is over there so I figured I'd be able to get by without the wrapping but I'll keep it in mind as an option if I have to resort to that.

 

 

 

 

 

Mine used to come on @ 3/4 and sometimes at 1/4 tank as GEE-OTTO said. After a while it just stopped coming on... I don't know if the fact that you're PZEV makes computer verry angry, but for me it stopped being an issue after a month or 2.

 

Did you clear the codes when they popped up or did you just leave them on?

 

 

Sent from my SGH-M919 using Tapatalk

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  • 3 weeks later...

My rallisport v1 header never made any codes pop up, but I wrapped it. And 3 days into my ceramic coated custom v3 header with no issues.

Btw, wrapping it voids warranty according to Mike. Ceramic coating is where its at :)

'08 Legacy 2.5i - hybrid intake - delta 1000 - E85 - magnaflow exhaust
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Thanks gee-otto, i remember reading the same thing from you in a couple other posts :)

 

A quick update:

After clearing the codes on Saturday night, the car sat till Monday. Upon starting the car up Monday morning to go to work, it took quite a few cranks before the car turned on which was a bit peculiar. The car ran pretty crappily during the 10 minute drive to work (wanting to stall coming to a stop at redlights, hesitating when stepping on the gas).

 

When starting the car to go home later that day, it started right up like normal again and I ran a couple errands before going home with the car running perfectly normal again (no more hesitation/wanting to stall at redlights).

 

The car also worked perfectly today as well. An interesting thing I noted was it being much easier to get a high MPG reading on the little clock readout thing. I usually drive with it on to try to keep my foot from getting too heavy around town. It may just be a coincidence, but it is a lot easier to keep at a high reading now after the car settled back into proper working order from Monday morning.

 

this is normal after clearing the ecu. turn the ignition to on without starting until the fuel gauge goes up, then start. Also the .2-.8v o2 sensor is your rear sensor, i could be wrong but pretty sure it is. If it is fluctuating like that it means a bad cat or bad sensor. Mine does the same and I have a oem cat on a 2007 that was burnt out from a misfire. The front o2 sensor should say wideband and runs around 2.7-2.8v. If you look at the test results in the torque app it should show you the catalyst monitor and what it detected. I think max is about 19 and mine usually is 25-30.

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hmm, i dunno what version of torque you have but all i have that would remotely make sense are O2 volts bank 1 and bank 2 but only bank 1 has data output that torque can detect.

 

correct me if im wrong, but i was under the impression that the fluctuating O2 reading im getting is from the lean-rich cycling that the front o2 sensor should be picking up.

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rear should stay at around .7v when engine is warmed up and not fluctuate, but I dont have a working cat to prove this right now. during the first 5 minutes or so it will switch .2v to .8v because the front is not being used to make air-fuel adjustments. the rear should not move once it is warmed up if the cat is doing its job.
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