o3nisoaso3

why wont the p0300 go away and i got a 2.5" catless dp... would that cause the p0135 or what?

BOOSSTED 06

for the p0300 have you checked your plugs

o3nisoaso3

replaced them with new stockers and also had the dealership do a ignition module and plug change... i just ran out of my warranty about 1500 miles ago.

409Cobalt07

that is a random missfire code right?

Joeyavhu

Yup.

boostnss

im getting the same p0300 code too

memphisr24

Weird thing is, my car throws the p0300 ALL the time...however the CEL light on the dashboard never goes on. Everytime I scan the car however, p0300 is displayed...very awkward...I delete the code each time but by the next time I scan the car for codes, it's back up...

p0135 is heater performance bank 1 sensor 1.....I believe that has something to do with the o2 sensor in the header...correct me if i'm wrong

boostnss

i don't scan mine to often but every time i do it's there my car is going into the shop saturday maybe they will figure it out

BLKLS

its posable that the stage 2 cams are setting that code at idle...if you have a heater code for the cat i'd just replace it.

jperris

the P0300 code is most likely caused by your cams. That code will be set if the computer detects a brief variation in crankshaft speed, calculated from the signal recieved from the ckp sensor. The stg 2 cams will cause your engine to run rough at idle, which makes the computer think there is a misfire, but won't be able to trace it to a specific cylinder. Otherwise you'd be getting P0301, P0302, P0303, or P0304 along with your P0300. Running those stage 2 cams without tuning is bad idea, but i guess not a huge deal if you don't mind some odd behavior from your engine.

the P0135 code has nothing to do with the cat. it indicates a malfunction in the heating circuit for the front o2 sensor. modern o2 sensors have heaters in them to warm them up faster to get the car into closed-loop operation sooner in an effort to reduce cold-startup emissions.

if you are getting this code, check to make sure that the wiring for the front o2 sensor isn't rubbing on anything (common issue on a car with bolt-ons), if no rubbing, you probably need an new front o2 sensor.

bottom line, a bad cat or even a missing cat will not set this code. it's an issue either with the o2 sensor or the wiring to the sensor.

Joeyavhu

A code like that is thrown, and then once the problem goes away, so does the CEL. If it quickly misfires bad enough, it would throw it and then disappear without you even noticing. It has done it on mine, grant mine is the 2.0, but how CELs come on are the same.

o3nisoaso3

figured something like that. i dont have a cat and figured the 2nd o2 would go off... ive been looking for a new 1st one

car is tuned and idles 800-900ish

XM15

Would a lightweight flywheel give you a P0300 code? I just had one installed, and now I am throwing that code. I've never had that before.

jperris

i think that might do it

o3nisoaso3

that could be my prob. thats when it first showed up and i asked quite a few ppl in a thread back in november but never got an answer...

XM15

If it is the flywheel, I wonder what we can do about it, short of removing it. And I'm definately not removing it.

That would be annoying not passing emissions because of a CEL due to a non-emissions part.

shortyheldberg

I know my 2.4 was throwing the same code po300 with my cai, what was happening was at the car wash the under carrage wash got the filter just at the tip and water or condesation would keep making me throw the code. If you have a cai I would check the filter. When I checked mine out it was barely visable but I did see the water stain and it looked dry. Now that I changed to the K&N it hasn't came back Remember it only take a little moisture to throw the code. At least that was in my case.

Fast Freddy

I threw a po300 right before I toasted my factory pistons.

XM15

I feel better now. lol

black06ss

i have been throwing it for quite some time now. mine came right after i put on my hahn catback, or maybe my header i cant remember. either way it could be caused by too little back pressure maybe. i also need to work on my tune so it could be in there somewhere.

o3nisoaso3

its probably a mix of a whole bunch of different things that can cause this code. id say that everyone is probably right with their problems but im not a tech so idk

XM15

I just heard back from the racing shop. I had the P0300 code before the install. I am due for a fuel filter change and I've got a feeling that is probably it.

o3nisoaso3

Got a P0420 now and still the random misfire P0300.

XM15

Well, the P0420 would be because you don't have a cat. I sometimes even get that with my high-flow.

SilverSS/SC

Mine sets the 0300 all the time . Clear it , its back within a day . Ive never been able to figure it out as I dont have any issues . Wierd thing is if I change my plugs the code goes away for a few thousand miles before it starts setting again I do have a aluminum flywheel , no clue if theres a corralation . I dont recall 0300 starting to set after I put the fylwheel in .