Need help with P0420

Discussion in 'Gen 2 Prius Main Forum' started by SB100, Sep 9, 2019.

  1. SB100

    SB100 Junior Member

    Joined:
    Jun 13, 2018
    5
    1
    0
    Location:
    Hanover PA
    Vehicle:
    2008 Prius
    Model:
    Base
    About 2 months ago I got the good ol P0420. My car is an 08 with 212k on her and does burn oil. I say she burns oil because I know the miles and that fact alone point to it being the CAT. But I can’t point to exactly what it is. Driving wise my MPG has dropped from 52 to about 45, she is definitely low in power and acceleration. Hills are horrible the engine bogs down and sounds terrible. The gas pedal is very hard showing a lot of engine pressure. All these made me believe it was a clogged CAT. The CEL will come on and go out a few days later most of the time. The thing that throws me off is it’s temperature dependent. When it’s hot out she has no power takes forever to get up to speed (especially with AC on) and will usually throw CEL. When it’s cooler outside it feels better, not as sluggish, but still not her normal self. That made me feel like maybe it’s an O2 but not sure so I thought I’d ask the best Prius community out there. CAT, O2, or something else ?
     

    Attached Files:

  2. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    2,919
    1,055
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
    Bummer... It's a bit early in mileage for this kind of problem and not sure what you can do short of replacement... There's some threads on here about cleaning attempts... And putting something in your gas tank to fix it seems pretty much debunked.

    So if it's not an 02 senor issue or recent recovery from too much motor oil, you're kinda out of options... Of course maybe someone will come along and offer up a way to extend the end of your catalytic converter's lifespan?
     
  3. Skibob

    Skibob Senior Member

    Joined:
    Sep 14, 2018
    2,682
    1,360
    0
    Location:
    Northern California
    Vehicle:
    2006 Prius
    Model:
    N/A
    I don’t know how your gas petal could get hard to push, it’s fly by wire. Basically a rheostat that sends a signal to a computer. Have you tried replacing the plugs and air filter, cleaning the MAF and the throttle plate? I would try that first and see what happens.
     
  4. SB100

    SB100 Junior Member

    Joined:
    Jun 13, 2018
    5
    1
    0
    Location:
    Hanover PA
    Vehicle:
    2008 Prius
    Model:
    Base
    By the gas pedal getting hard I mean by how hard I have to push it to get it the car to accelerate, which since the CEL started coming on is a lot more than it used to be. I have replaced plugs and air filter, may have to look at the throttle plate
     
  5. Skibob

    Skibob Senior Member

    Joined:
    Sep 14, 2018
    2,682
    1,360
    0
    Location:
    Northern California
    Vehicle:
    2006 Prius
    Model:
    N/A
    And clean the MAF also. About as close to a tune up as these cars get.
     
  6. chelvis

    chelvis Member

    Joined:
    Oct 27, 2011
    64
    41
    0
    Location:
    Long Valley, NJ
    Vehicle:
    2005 Prius
    Model:
    Five
    I replaced the cat on my 05 Prius at 312,000 two weeks ago (yes this is a true statement), bought aftermarket Bosal from Rockauto.
    I had the P0420 code for about three years, squeaked through NJ inspection last year (an act of God when the light was off going through emissions inspection). I did have crappy uphill performance and my engine does consume some oil. I did the plugs, coils, MAF clean about 18 months ago, result was the performance and mileage better, but still had the code and CEL on. Since the cat change, the code is now gone, mileage appears better, but want to get a bigger sample size before declaring major victory.
     
    PriusCamper likes this.
  7. Frijjj

    Frijjj Junior Member

    Joined:
    Aug 9, 2019
    38
    17
    0
    Location:
    Runcorn, UK
    Vehicle:
    2008 Prius
    Model:
    N/A
    I have the same P0420 code. Looking through the forum people have suggested that worn engine mounts might cause this problem as the engine rocks breaking the seal between the manifold (header? in the USA) and the down pipe of the catalyst.

    Also with burning oil you could have a jammed open PCV dumping oil into the throttle body. I'm looking into putting an oil catch can between the PCV and the throttle body but I'm not sure on where the best place to attach it is. I'd look below the butterfly valve in the throttle body and see if you have a lot of oil. I replaced the PCV valve (and broke the end off coil pack 4 as I was too lazy to remove it. Don't be lazy. ooops)

    172925_IMG_0095.jpg



    nssdiver has his as above but I'm not sure where it's attached. I've ordered a catch can like this and I'm hoping I can figure out a way of attaching it.

    158946_IMG_3235.jpg
    158947_IMG_3236.jpg

    This was in the gen3 catch can thread but off a gen2, wire wool used to provide a baffle.
    Oil Catch Can, Eliminate that knock! | PriusChat


    This oil could then be getting passed into the exhaust and poisoning the catalyst. My catalyst look pretty new. I live in a salt area so it should look bad but it's in good shape. People are saying they only last 30k miles or so if you don't fix the problem I would say that looks to be the case from my car. I have no history on it so It's all guesswork.

    One thread did suggest "CataClean Liquid Science Petrol Hybrid Car Engine Fuel & Exhaust System Cleaner" but I've not used it yet, with the catch can in place it could be an easy fix if it removes the oil blowing through. I'm also going to try an engine oil flush to see if that can help the rings seal better as this was a recall on some later engines.

    the ring problem

    Toyota's engine flush:



    I'm interested in any further opinions. If the cataclean is a waste of money then it will have to be a replacement cat but in the UK a full OEM cat system is £100 ($120-125) so it's not too bad, the back box looked worse than the cat on mine so got the back box for £50 but I'll risk the cleaner for an experiment if there's no data.
     
  8. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    2,919
    1,055
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
    FYI: There's a not normal situation in dealing with '08 Gen2 exhaust gas re circulation system... Which is to say that the system doesn't exist in the same way as normal cars.. In a gen2 it's done via valve timing. I like that idea in that it makes then engine design more simple. It's also why I like Gen2 more than Gen3
     
  9. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    2,919
    1,055
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
     
Loading...