New CAT - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
Problems and Service Talk about any mechanical problems you are having

 
LinkBack Thread Tools Display Modes
post #1 of 10 (permalink) Old 11-08-2013, 02:56 AM Thread Starter
Prospect
 
Join Date: Oct 2013
Posts: 20
New CAT

My 06 Cobalt (2.2 DOHC) was throwing a p0300 code for about two months before I got it fixed. It ran fine for about two weeks and is now throwing a p0420.

I cleaned the throttle body, no luck. It also has a high idle, around 1400.

Did the CAT go bad running it with the p0300 code?

Is there a way to test the CAT?

What is the best replacement CAT to get and where?

Thanks.

Joel

---------- Post added at 05:56 AM ---------- Previous post was at 05:44 AM ----------

Was wondering if it could be the "Mass air flow sensor". I did spray some electronic part cleaner on it, is there a way to test this?
joele8 is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old 11-08-2013, 05:45 AM
YourCobalt of the Quarter Winner
YourCobalt of the Month Winner


 
BankerBalt's Avatar
 
Join Date: Oct 2010
Location: Eagan MN
Posts: 4,647
Garage
The cat could have went bad due to the misfires and unburnt fuel clogging it up. Look for a magnaflow cat

Forged L61 BW S252 Turbocharged Showoff Thread
BankerBalt is offline  
post #3 of 10 (permalink) Old 11-08-2013, 05:57 AM
Cobalt Specialist


 
Join Date: Jun 2011
Location: Charlotte, NC
Posts: 1,145
The p0420 code is catalyst efficiency is bad. From the mechanical/electrical misfiring of unburned fuel particles will go straight to your catalytic converter. Hydrocarbons aka Fuel atomization from the injectors clogged up your cat converter and causing the rear oxygen sensor to not read the right amount of c02 levels will trigger that code and run into "limp" mode. Its nothing more than just staying in open loop status to run rich to keep your vehicle alive.

If you were planning on going abouts a new cat converter and Bankerbalt's idea of a magnaflow performance cat, it "must" be a 3-way platinum bedding style of cat in which they offer. I would highly suggest fixing your p0300 (random engine misfire) first, otherwise that new cat will go bad once again. The p0300 can be from improper ignition timing, clogged injectors, wrong octane level, something that is not meeting the original setup for the combustion cycle of the engine.

I know GM offers a full downpipe with the cat converter built in, but its asking around $840 new. Or just pull one out of a junkyard for a lot less than that, but you risk on if the cat is good or not. ZZP offers a 2.5" catted downpipe and people on here love it for the non p0420 code, just include the 400 cell cat they offer under the options if you plan on purchasing one. Hope this helps.

2009 Cobalt LS XFE U74
Mods: K&N Typhoon Intake, Option Cat-Back Exhaust, Cosmo Short shifter, Maxxim Ahead 17X7's, MPx shorty antenna, FE5 Strut/shocks, Tein S Techs, Moog endlinks, Moog spring seaters, ZZP shorty header, LSJ downpipe, LNF front grille
5t3alth is offline  
 
post #4 of 10 (permalink) Old 11-08-2013, 06:03 AM Thread Starter
Prospect
 
Join Date: Oct 2013
Posts: 20
Thanks for the replies.

The p0300 code is gone, replaced plugs, boots, module.

Would a bad CAT cause it to have a high idle?
joele8 is offline  
post #5 of 10 (permalink) Old 11-08-2013, 06:15 AM
Cobalt Specialist


 
Join Date: Jun 2011
Location: Charlotte, NC
Posts: 1,145
Quote:
Originally Posted by joele8 View Post
Thanks for the replies.

The p0300 code is gone, replaced plugs, boots, module.

Would a bad CAT cause it to have a high idle?
Glad you got that code gone, Your car is in open loop mode with a CEL on. For your p0420 Catalyst Efficiency code, your car may act a bit funny, such as engine temp will not set to normal operating temps, go through gas much quicker and fuel economy decrease up to 5 mpg's, fuel odor coming by tail pipe, and possible idles of 900 rpms-1100.

If your idle is sitting after 5 minutes above 1200, you have something else that's causing it, vacuum leak, dirty air filter. Just check your hoses and air filter to see if any dirt/debris or cracks, abnormal wear.

2009 Cobalt LS XFE U74
Mods: K&N Typhoon Intake, Option Cat-Back Exhaust, Cosmo Short shifter, Maxxim Ahead 17X7's, MPx shorty antenna, FE5 Strut/shocks, Tein S Techs, Moog endlinks, Moog spring seaters, ZZP shorty header, LSJ downpipe, LNF front grille
5t3alth is offline  
post #6 of 10 (permalink) Old 11-08-2013, 06:20 AM Thread Starter
Prospect
 
Join Date: Oct 2013
Posts: 20
yea the idle stays up there, will check everything. thanks.
joele8 is offline  
post #7 of 10 (permalink) Old 11-08-2013, 06:41 AM
Cobalt Specialist


 
Join Date: Jun 2011
Location: Charlotte, NC
Posts: 1,145
no problem. Typically a vacuum leak will not trigger a DTC or CEL since its mechanical.

2009 Cobalt LS XFE U74
Mods: K&N Typhoon Intake, Option Cat-Back Exhaust, Cosmo Short shifter, Maxxim Ahead 17X7's, MPx shorty antenna, FE5 Strut/shocks, Tein S Techs, Moog endlinks, Moog spring seaters, ZZP shorty header, LSJ downpipe, LNF front grille
5t3alth is offline  
post #8 of 10 (permalink) Old 11-08-2013, 05:52 PM
Super Moderator


 
Plain Jane's Avatar
 
Join Date: Mar 2013
Location: Montreal, Quebec
Posts: 3,860
Garage
Your car will be a thirsty, gutless pig when the MIL is on, not fun in any situation. Did you follow the correct procedure when you cleaned your throttle body? Might need a relearn if you botched it. Good luck.

'07 Eclipse GT build thread - 280whp, 254wtq
Plain Jane is offline  
post #9 of 10 (permalink) Old 11-12-2013, 01:34 PM Thread Starter
Prospect
 
Join Date: Oct 2013
Posts: 20
The idle has settled down, around 900. Took everything off after the throttle body and made sure there were no leaks. Also changed the air filter.

However the CEL for code P420 is still on.

A new sound arose, at around 35 MPH (and up) the car makes a hum, loud enough to be heard over the radio. The hum is most noticeable when the car is cold.
joele8 is offline  
post #10 of 10 (permalink) Old 11-13-2013, 02:53 PM
Cobalt Specialist


 
Join Date: Jun 2011
Location: Charlotte, NC
Posts: 1,145
p0420 will not be resolved until a new cat converter is installed and code has been cleared. Good to hear your idle is now roughly in the right area, is any accessory turned on such as A/C or heat? That will cause an engine load to increase RPM.

My car does that too, but at 5th gear on 45 mph area, but mine shakes the roofline, but that's caused by harmonics from the transmission. You have to realize that your car has lots of vibrations and hums that the human ear cannot hear nor feel. Sometimes it can be from gears or mechanical moving parts, like for a good example, a camshaft spinning without pistons compressing is annoying loud, we hear it on a engine dynamometer when breaking in a camshaft for racing applications, but when the engine is completely turned over and running, you wont hear the camshaft anymore.

2009 Cobalt LS XFE U74
Mods: K&N Typhoon Intake, Option Cat-Back Exhaust, Cosmo Short shifter, Maxxim Ahead 17X7's, MPx shorty antenna, FE5 Strut/shocks, Tein S Techs, Moog endlinks, Moog spring seaters, ZZP shorty header, LSJ downpipe, LNF front grille
5t3alth is offline  
Sponsored Links
Advertisement
 
Closed Thread

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome