Chevy Cobalt Forum banner

Status
Not open for further replies.
1 - 14 of 14 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
A few months ago, my car threw the TC P0420. I didn't have the money to deal with it then, but over the last 6 weeks, I've been trying everything I can to no avail.

First, I took it to the shop. They charged me 400 for an upstream sensor. CEL came back on. Then, they said I had to replace the cat. So I buy one off Ebay (premium based on manufacturers specs) and that didn't work. Code came back. So finally, I figure there is only one possible problem left. The downstream O2 sensor. So I buy one and replace. CEL came back! At this point, I'm confounded so I research some more, and try the spark plug savor MOD. Essentially, it pulls the sensor out of the stream. Runs rough until computer calibrates, then it starts running REAL bad. Not shifting correctly, at the right RPM's, and trans makes dropping noise when I shift to D or R. So I climb back under there and pull the MOD off. I had unplugged the battery while removing that MOD, but not 10 minutes into test drive, the CEL came back on. I figure the computer needs to relearn the operation protocols.

The engine runs a little better after removing MOD, but trans is still kinda slamming into 2nd, and a tiny bit in 3rd and 4th. I plugged the monitor in this morning and it gave me 10 different, exhaust/vacuum related codes. I figured it is still figuring stuff out so I reset it, and test drove it again. 15 minute test drive and no problems except for the slight gear slippage into 2nd. I turned the car off and when I turned it back on, CEL reposted. Typically, it takes a week for the CEL to throw the P0420, but now, my CEL hit fast.

What am I gonna do about this thing? I bought the parts, and did all the work myself cause I'm broke. When I do take it to the garage, They are gonna create a huge list of vacuum leaks, and god knows whats else to try to charge me for. Any insite, or reassurances would be totally appreciated.
 

·
Super Moderator
Joined
·
11,821 Posts
Maybe you didn't know this, so I'll post it for you because a new cat can set the 420 code for the first 100 miles or so.

DTC Descriptor
DTC P0420: Catalyst System Low Efficiency


Circuit/System Description
Important: A new converter with less than 100 miles on it may set DTC P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

A 3-way catalytic converter (TWC) controls emissions by converting hydrocarbons (HC) and carbon monoxide (CO) into carbon dioxide (CO2), and oxides of nitrogen (NOx) into nitrogen. The TWC also stores oxygen. When the listed driving conditions are met, the Catalyst System Efficiency test will run. The powertrain control module (PCM) monitors this oxygen storage capacity by comparing the pre and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific driving conditions. The PCM compares the pre and post-catalyst oxygen sensor signals to determine if the oxygen storage capacity of the catalyst is degraded.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #3
Thanks for the response.

Yeah, I was aware of that and gave it almost 400 miles after cat replacement.
 

·
Super Moderator
Joined
·
11,821 Posts
It might be the ground connection of the HO2 circuit then.
 

·
Registered
Joined
·
3,229 Posts
Check the "EXH" fuse under the hood in the engine compartment fuse box. This is the fuse for that circuit. I remember mine blew after my build and it was causing all sorts of issues. It is connected to the evap solenoid as well as the upstream (pre-cat) O2 sensor and one or two other things. Make sure the O2 sensor is properly plugged. I still get codes from my upstream O2 sensor after my build but for me it's nothing major and I know what it is more or less.
 

·
Super Moderator
Joined
·
11,821 Posts
The HO2s find there grounds through the "PCM" or "ECM" depending on the year of your Car. So lots of stuff would be screwed up if it was this ground. But like BBoy says check the fuses or the connector at the "PCM" or "ECM".
 

·
Registered
Joined
·
922 Posts
what brand o2 sensor did you get. There have been a ton of problem with the Bosch o2 sensors. Best way to go is OEM. 400 for a dealer to do an o2 sensor is robbery. The o2 sensor cost 50+/- a few and it takes 15 mins to change it. 1 hr maint at say 80 per hour. At the absolute most is should have costed through the dealer or any shop is 200, and thats on the extreme high side
 

·
Registered
Joined
·
3,229 Posts
Check Rockauto. com, they have O2 sensors including the ACDelco OEM ones. They also have very reasonable prices. I believe the next sensor I try will be an ACDelco one like stock. Hope it works as it should.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #12
Update
The downstream mod blew the EXH fuse. I replaced it and checked all the others. Operation and tranny problems corrected. Two days later, the cat posts and the MIL comes on. P0420 Low cat.

I'm dying over here. Still don't have the emissions inspection sticker after 3 months.

Regarding the sensor manufacturer, it is a Danko.
 

·
Registered
Joined
·
3,229 Posts
Update
The downstream mod blew the EXH fuse. I replaced it and checked all the others. Operation and tranny problems corrected. Two days later, the cat posts and the MIL comes on. P0420 Low cat.

I'm dying over here. Still don't have the emissions inspection sticker after 3 months.

Regarding the sensor manufacturer, it is a Danko.
...what mod did you do to the downstream O2 sensor?!?!
 

·
Registered
Joined
·
6 Posts
Discussion Starter #14
Reply

Spark plug defouler. Drilling the bottom out of the defouler allows room for the sensor probe to fit in, but in effect, the defouler pulls the sensor probe out of the exhaust downstream. Some guys said it worked, but mine just ran like total dogsh!t afterwards.
 
1 - 14 of 14 Posts
Status
Not open for further replies.
Top