Thread: Got some codes read, not sure what they mean.

Car threw some codes today, had them read, couple were no big deal, but these two caught my attention.

Code P1811

Definition: Maximum adaptive and long term shift.

Explanation: The ECM has detected the shift execution time has exceeded the required shift time period.

Probable Cause:

1. Trailer towing may falsely set code

2. Low line pressure - plugged filter or pump

3. Computer relearn may be required


Code P0420

Definition: Catalyst eficiency low-bank 1

Explanation: The oxygen sensors monitor the Catalytic Converters ability to store oxygen.

Probable Cause:

1. Catalytic converter defective (failure possibly due to #2, 3, or 4)

2. Engine misfire or running condition

3. Large Vacuum Leak

4. Engine oil leakage into exhaust-valve guide seals, piston rings



OK, how do I go about figuring out the actual reasons for these codes being thrown. Particularly the second one. Could code P0420 be the cause of some overheating problems I've been having? Not sure how to go about doing these step by step...


Thanks for any help

OK I'll tap on the cat when it gets cold. Would a bad cat cause overheating?

Car Maintenance : Can a Bad Catalytic Converter Make a Car Overheat? - YouTube


This guy says clogged or bad catalytic converters can cause overheating...

Me and a friend have the exact same car, we will both be driving around, short drives, long drives, etc. and my vehicle gets MUCH hotter than his, my engine bay feels hotter and my car runs hotter. I'm thinking the backup of the heat from the exhaust is a pretty decent explanation as to why it's all so hot. Does it cost a lot to replace a cat?


As far as the shift kit goes that you mentioned, where can I pick one up? And is it a relatively easy self install?

I got that same code p0420 i used that cataclean treatment it help a little the check engine light went out and has not been back on but when i hooked up my scan tool the p0420 was still stored took the car my mechanic he confirmed the cat is going bad the estimate was $1000 is that to much or about right? they are ordering a direct fit cat from the dealership (2005 grand Prix GTP under 120,000 miles) Thanks guys

Originally Posted by cease1981

I got that same code p0420 i used that cataclean treatment it help a little the check engine light went out and has not been back on but when i hooked up my scan tool the p0420 was still stored took the car my mechanic he confirmed the cat is going bad the estimate was $1000 is that to much or about right? they are ordering a direct fit cat from the dealership (2005 grand Prix GTP under 120,000 miles) Thanks guys

$1000? You could save a lot of money doing it yourself if you have the means to do so. I replaced mine back in April, but my buddy has a lift in his garage. Took an hour if that. Even if you can't do it you could just buy one for a lot cheaper and have your mechanic install it. Here's the one I got. More Information for EASTERN CATALYTIC 50358 Save money, don't buy from the Stealership.

Originally Posted by Ohara

$1000? You could save a lot of money doing it yourself if you have the means to do so. I replaced mine back in April, but my buddy has a lift in his garage. Took an hour if that. Even if you can't do it you could just buy one for a lot cheaper and have your mechanic install it. Here's the one I got. More Information for EASTERN CATALYTIC 50358 Save money, don't buy from the Stealership.

Thanks that's exactly what I'm going to do, do you know if the cat come with the gaskets or do i have to buy that separately

Originally Posted by cease1981

Thanks that's exactly what I'm going to do, do you know if the cat come with the gaskets or do i have to buy that separately

Mine came with front and rear gaskets.

Where I live they don't care about emissions. Well, I shouldn't say they don't care, but they don't check them and aren't required for a yearly inspection. Gonna just grab a hacksaw in the morning and cut the damn thing off.

Originally Posted by Ohara

Mine came with front and rear gaskets.

Thanks a lot by taking your advice i saved a lot of money i got the exact same catalytic converter you bought $192 after tax and $80 to have it installed

Where do you suggest getting a cat from thats legal in California?

People talk about emissions testing. First I ever heard it in my 30 years was about a month ago.

Originally Posted by Fivefingerdeathpunch

I wouldnt if I was you.


Unless you want the car to get some real crap tastic mpgs. No cat and your car will just dump fuel likes its pouring it down a drain.

I gained 3-4 mpgs with no cat and no 02s , maybe I got lucky ?