P0420 code

T

Trigg

Member
So on this lovely rainy morning I drove my wife's jeep into work ( '12 JKU auto ) and the CEL came on. I busted out my handy-dandy code reader and got P0420 left bank CAT Eff. I viewed the live data and couldn't tell any noticeable laziness between the up and down streams during the switches between O2 sensors. I crawled underneath and did a quick check of the wires they seemed intact. I'll have to wait till I get home to break out the volt meter and double check them when I get home.

Its got just over 80k miles and Im pretty sure the spark plugs haven't been changed before. I've had the code pop on my TJ before when I had warn out plugs. Think this could be a possible cause for the code?

Air filter is about 10k miles old and it still looks really good.

Only thing I know that is needs at this time is a oil change and that only cause the reminder came up yesterday.

I remember reading about a TSB about head issues but I'm pretty sure that was in the early 3.8L models. Does this ring a bell to anyone?

I have not noticed a drop in fuel efficiency. It runs just as well as the day we bought it, nothing out of the ordinary.
Considering its just the one code and not both banks I'm leaning towards the upstream O2 sensor. What are yall's thoughts?
 
P

plext0r

New member
Our 2008 JKU threw a P0430 (same issue as yours but Bank 2). I found a cracked left exhaust manifold which I replaced about 2-3 weeks ago. The CEL came back on, so I plan to follow the rest of this helpful checklist. I need to buy a gap tool and check or replace the plugs; we just bought this Jeep in June with 140K miles and I have no idea if/when the spark plugs have been replaced.
 
mudmobeeler

mudmobeeler

Caught the Bug
Trigg said:
So on this lovely rainy morning I drove my wife's jeep into work ( '12 JKU auto ) and the CEL came on. I busted out my handy-dandy code reader and got P0420 left bank CAT Eff. I viewed the live data and couldn't tell any noticeable laziness between the up and down streams during the switches between O2 sensors. I crawled underneath and did a quick check of the wires they seemed intact. I'll have to wait till I get home to break out the volt meter and double check them when I get home.

Its got just over 80k miles and Im pretty sure the spark plugs haven't been changed before. I've had the code pop on my TJ before when I had warn out plugs. Think this could be a possible cause for the code?

Air filter is about 10k miles old and it still looks really good.

Only thing I know that is needs at this time is a oil change and that only cause the reminder came up yesterday.

I remember reading about a TSB about head issues but I'm pretty sure that was in the early 3.8L models. Does this ring a bell to anyone?

I have not noticed a drop in fuel efficiency. It runs just as well as the day we bought it, nothing out of the ordinary.
Considering its just the one code and not both banks I'm leaning towards the upstream O2 sensor. What are yall's thoughts?
Click to expand...

Usually a cat efficiency code means that the cat is failing. The O2 sensors will usually throw their own codes. What normally happens is the internals to the cat start to break up and will shift around causing the exhaust to not flow through properly.
 
T

Trigg

Member
Seems a little early in its life for a bad cat but ill get the stethoscope out and listen for any loose material. Ill check the manifold as well, thanks for the help.
 
mudmobeeler

mudmobeeler

Caught the Bug
Definitely check it out before replacing.

I've seen them fail with 50k miles on them before. Anything is possible.
 
WJCO

WJCO

Meme King
Typically a 420 code with no others is a failing cat. Sometimes it can plug and the material won't be broken. If indeed it is the cat, it falls under Federal Emissions warranty of 8 years or 80000 miles unless it's modified or physically impacted.
 
MTG

MTG

Caught the Bug
Trigg said:
So on this lovely rainy morning I drove my wife's jeep into work ( '12 JKU auto ) and the CEL came on. I busted out my handy-dandy code reader and got P0420 left bank CAT Eff. I viewed the live data and couldn't tell any noticeable laziness between the up and down streams during the switches between O2 sensors. I crawled underneath and did a quick check of the wires they seemed intact. I'll have to wait till I get home to break out the volt meter and double check them when I get home.

Its got just over 80k miles and Im pretty sure the spark plugs haven't been changed before. I've had the code pop on my TJ before when I had warn out plugs. Think this could be a possible cause for the code?

Air filter is about 10k miles old and it still looks really good.

Only thing I know that is needs at this time is a oil change and that only cause the reminder came up yesterday.

I remember reading about a TSB about head issues but I'm pretty sure that was in the early 3.8L models. Does this ring a bell to anyone?

I have not noticed a drop in fuel efficiency. It runs just as well as the day we bought it, nothing out of the ordinary.
Considering its just the one code and not both banks I'm leaning towards the upstream O2 sensor. What are yall's thoughts?
Click to expand...
Just went through this myself last week.

http://wayalife.com/showthread.php?1585-The-building-of-knuckles&p=624677&viewfull=1#post624677

Bad Cat. Covered under warranty.

Note: They changed the O2 sensors as well at the time and they were not covered under warranty. Got a call back the next day and had to pay $124. Just giving you a heads up.

Mine is a 2012 with 52K miles on the clock.

Edit: And I believe the federal emissions warranty is only good for 8 years and 80K miles. Good luck!
 
T

Trigg

Member
Still at work but I haven't been able to crawl under to hear or check anything else with the daylight. I was reading my mopar coverage and its a little miss leading but I appear to still be covered. My only thing is I don't see a exhaust section and its not under engine on the website. If its not covered then ill just buy one and install it my self. either way made appointment for tomorrow need to get a safety inspection done for registration anyhow. Wish me luck.


Plan Summary for ARBEGAST
Plan Number 39555183
VIN Number 1C4HJWEG0CL123339
Description CERTIFIED PRE OWNED VEHICLE PROGRAM
Expires on 2021-12-23 or 999999 miles
Start Date 2014-12-24
Deductible Per Repair $0.00
Towing Coverage $0.00
Rental Car Allowance $0.00 per day for a maximum of $0.00


Plan Summary for ARBEGAST
Plan Number 39555183
VIN Number 1C4HJWEG0CL123339
Description CERTIFIED PRE OWNED VEHICLE PROGRAM
Expires on 2018-11-21 or 100000 miles
Start Date 2011-11-22
Deductible Per Repair $100.00
Towing Coverage $100 Roadside Assist 800-521-2779
Rental Car Allowance $35.00 per day for a maximum of $175.00
 
T

Trigg

Member
Well had the appointment at the dealer today. Left the house and the light went off. Got to the dealer told them about the light going off and gave the Tech the code. Comes out a few minutes later and says he can't find anything wrong. We'll while he was tinkering I was chatting with parts guys and one of the service managers. Service manager laughed asked how many miles it had and was like well if the light comes back on bring it back. Ill go ahead and put the 80k waver in the system as a prior issue.

Didn't figure out the issue but atleast I got in good standings with the service manager.
 
WJCO

WJCO

Meme King
Trigg said:
Well had the appointment at the dealer today. Left the house and the light went off. Got to the dealer told them about the light going off and gave the Tech the code. Comes out a few minutes later and says he can't find anything wrong. We'll while he was tinkering I was chatting with parts guys and one of the service managers. Service manager laughed asked how many miles it had and was like well if the light comes back on bring it back. Ill go ahead and put the 80k waver in the system as a prior issue.

Didn't figure out the issue but atleast I got in good standings with the service manager.
Click to expand...

That's awesome. Next time that code pops up, snap a photo of it anyway. At least he was cool enough to do that. When I wrote service years ago and a customer had an issue just prior to warranty expiring, I would create a repair order for them with the current 'in warranty' mileage and just hold on to it. That way when they came back, we had something to go off of. I hope that they take care of you. With all the save-the-world tree-hugging eco-terrorists out there, if they're so worried about emissions, there should be programs in place to take care of the catalytic converters if they fail slightly outside the warranty time/mileage.
 
boostdtalon

boostdtalon

New member
Ok I need to ask for help since someone has already had similar issues. We've had the exhaust manifolds replaced, precat, and the main cat just this past week. Code came back today. Only been the P0420 code. I was planning to do spark plugs soon. Not sure what else to check.
 
WJCO

WJCO

Meme King
boostdtalon said:
Ok I need to ask for help since someone has already had similar issues. We've had the exhaust manifolds replaced, precat, and the main cat just this past week. Code came back today. Only been the P0420 code. I was planning to do spark plugs soon. Not sure what else to check.
Click to expand...

Being that it's a catalyst efficiency code, the only things I can think of would be the downstream o2 sensor (which would usually set another code along with the p0420) or a wiring problem or pcm for that same sensor. Any of those should set another code, but take a look. PCM may be covered under 8/80 warranty.
 
D

Drdiesel1

New member
Possible Causes
(K902) O2 SENSOR 1/1 RETURN CIRCUIT SHORTED TO GROUND
(K904) O2 SENSOR 1/2 RETURN CIRCUIT SHORTED TO GROUND
(K902) O2 SENSOR 1/1 RETURN CIRCUIT OPEN
(K904) O2 SENSOR 1/2 RETURN CIRCUIT OPEN
EXHAUST LEAK
ENGINE MECHANICAL CONDITION
AGING O2 SENSOR
CATALYTIC CONVERTER

Exhaust leaks from exhaust manifold cracks are the number 1 COF on lower mileage vehicles
 
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