P0420 code! WHATTT

[dmahlikGT]

For a few months now my check engine light has been on.I had a head job done back in may due to the infamous coolant leaking into the heads.Since then I have noticed a problem getting slighty worse by the weeks.when I start up my car it idles crappy until its warmed up. Then if I step on it at about 2-3 gear or 50-60mph it starts hesitating and jerking for more speed.Always happens.Seems to happen faster and worse when the car is hotter.I had the code read a few weeks ago and it was p0420.I changed my cat.im thinking either o2 sensor or fuel filter.Any ideas?

[grandprix85]

Check your MAF. I had the same symptoms with my car. I replaced my MAF and it stopped.

[ls6velless454]

Usually that code it related to your gas cap being bad/evap system it could even be a bad purge solenoid or vacuum line off the engine.

[dmahlikGT]

hmmm.those sound like possibilities especially the MAF.I'll see try those if the problem still persists.thanks guys

[dmahlikGT]

Oh also when I got the code scanned it specifically said catalytic inefficiency/bank 1 or something like that.Not sure if that makes a difference.

[01gpgt01]

p0420 is Cat code, Rear 02 issue. Replacing the maf will do nothing.

[dmahlikGT]

The 1st thing i thought of after my new cat,the rear 02 sensor.thanks man

[gtpinsc]

plugs? wires? ICM? coils?

[Echo1999]

Time to suspect that it could be a bad PCM.

[gtpinsc]

Time to suspect that it could be a bad PCM.

how so? theres alot of other things it may be.. could be a ****ty gasket job and coolant is making its way to a cylinder.

[dmahlikGT]

nope guys.the mis was a simple fix.my spark plug heat sheild was sparking with a bolt which pulled from the spark plug itself causing the mis.lol.i just took it off and it pulls hard again with no mis.back to the p0420 code,would a bad 02 sensor cause the engine idle to surge a little when accelerating?

[TorqueAutoMotiv]

A highflow cat can kick a 420 code rear o2 can kick a 420 code and so on
high flows arent as efficient as standard cats so it will still kick the code on some cars

Also depends how your tune is to test sscan your rear o2 sensor it should stay steady under 400 mili volts
if its higher or bouncing around thats your issue