Check Engine Light Keeps Coming On

[jersanter]

I have a standard 2006 V6 3.8L 4 dr Grand Prix Sedan. 105,600 miles

In June I failed emissions for a P0420 cat efficiency code. Replaced the cat.

A week later, same P0420 code came back. Replaced upstream O2 sensor.

A week Later, I was getting the “Check Gas Cap” from the dash board message center. That had happened in the past but I just replaced the gas cap and it went away. Anyway, check engine light came on again as well. P0455 code for large EVAP leak. Had smoke test performed and found vent valve cover and solenoid needed replacement. Should add terrible gas mileage also with this round of issues.

3 days later, check engine light comes on again. No check gas cap this anymore. My mpg is suffering a little not as bad as it was previously. I’m out of money!!! What the hell could be causing it this time? I’m having the code checked today, but I’m pretty close to ghosting this car into a quarry and reporting it stolen No issues at all until 105,000 miles.

[Mirraco]

get new gascap?

I had p0440 code come up on my 00 gt, had to replace egr purge valve, easiest roadside work i have done and engine code went away, i also thought it was gascap until i followed the fuel line and seen a very warn out tube, replaced it and ses light is gonezo.
With a 00p0455, the most common repair is to: Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back. Otherwise, replace the gas cap, and/or Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary

Read more at: http://www.obd-codes.com/p0455
Copyright © OBD-Codes.com

[jersanter]

The P0455 code is gone. I no longer get the check gas cap notification. I'm checking code this morning and will confirm back for further discussion.

[jersanter]

I once again have a P0420 code for cat efficiency. Again, cat was replaced with a direct fit cat. O2 sensor was replaced. This code says bank 1. Any ideas? The guy that put the cat on is going to look at it in great details on Monday. Hoping it's something that is warrantied.

[theaceofspades]

Shoulda replaced the downstream not the upstream

[Scottydoggs]

what cat brand did you get? if its high flow theres the issue. its needs a anti fouler or two installed to move the rear o2 out of the pipe some to trick it into working.

[stealthee]

Shoulda replaced the downstream not the upstream

This. Upstream is pre-cat, downstream is post cat. You are getting the code because you replaced the wrong o2.

[jersanter]

This. Upstream is pre-cat, downstream is post cat. You are getting the code because you replaced the wrong o2.

Would that cause the cat to go bad? I’m being told this morning that they put a defective cat on. Okay great but why is it defective? Bad part or did something cause it to go bad in not even 2 months? I’m going to have the downsteam O2 done on it also. They said they would make the call after the cat was put on, but I’m telling them to replace it. I’m tired of dealing with it, but I need to get her to go another 20-25k miles.

[Scottydoggs]

bad up stream o2 makes the engine run rich, ala over fueled, that clogs the cat fast.

i bet your mpg are in the crapper too.

[stealthee]

It sounds to me like they don't even know what they are talking about. How do they know they put a defective cat on? Sounds ridiculous.

Replace the downstream o2 and reset the code. Don't replace the cat until you can verify it is indeed bad.

[BillBoost37]

The cat isn't defective, their level of knowledge is defective.

GM has very tight tolerances on the expectations of change from pre to post cat. Therefore if you don't replace with a rocking kick butt nearly GM cat, you will sooner or later end up throwing the P0420 code based on the cat not doing a good enough job. Doesn't mean it's defective at all. It means the cat isn't doing a good enough job to meet the parameters set in the pcm.