Check Engine light frustration

trivet · **Posted:** Tue Feb 23, 2016 4:51 pm

Hi all,

Looking for some help. I have had a persistent CEL issue for the last several months. My 2010 KK is throwing code P0420 (o2 sensor, downstream) – I’ve replaced BOTH downstream o2 sensors, reset the code, and the next day it will pop up again. I disconnected the battery overnight, and it was fine for a day, then again with the same code. :furious:

A little history, not sure if it’s pertinent or not. Last summer I was cleaning my engine (filthy from the Michigan winter) and the Jeep starting running REALLY rough, spitting and sputtering, then stalling – CEL code was for a faulty ignition module. Seems my engine is not very water resistant – no water got in the intake, it was 2 ignition modules that were flooded. I pulled them all, dried them out, got all the water out of where they install (pardon the lack of technical terms) - and she started right up and ran perfectly again. The next day I go the same CEL fault code – I figured I fouled the O2 sensors with how poorly the engine ran, so I didn’t think much of it. Replaced the left bank downstream, reset the CEL light, came on again the next day. It was a few weeks before I had a chance to change the left bank sensor. Once again, reset the CEL, was on again the next day.

So I figured it was beyond my backyard mechanic skill set, took it to my (real)mechanic, he got the same fault codes, replaces the offending O2 sensor, same thing. Next day - same code. :banghead:

I can’t get the darn thing to stay off! Also, when the CEL is on the ECO “ON” setting (odometer setting) doesn’t work – no idea if this means anything, but wanted to put it out here as well.

What am I missing? Is this a common issue with KK’s? Or did I irreparably damage my Jeep?

Thanks in advance for any suggestions,

Tim

tjkj2002 · **Posted:** Tue Feb 23, 2016 7:19 pm

P0420 is not a O2 sensor code.

You need a new bank 1 cat,and if 1 failed might as well replace the other 1 at the same time.If your under 80,000 miles(and in the USA) that cat is free from the dealership via federal emission warranty.

ajohns1288 · **Posted:** Tue Feb 23, 2016 9:05 pm

Expanding on what tjkj said, the P0420 code just means that the readings from the downstream O2 sensor look bad. This can be due to a faulty sensor, bad wiring, or bad cat. Which coils did you have problems with? It sounds like the coil issue allowed unburnt fuel into the cat which in turn reduced the efficiency.

trivet · **Posted:** Tue Feb 23, 2016 10:30 pm

Thank you - that makes sense. I didn't even think the cat might be bad, not the sensor.

And I have 130,000 miles on the Jeep, so I'm way out of warranty unfortunately.

What options do I have? Replacing 1 or both cats will be prohibitively expensive - (a quick Google search shows that this will be VERY expensive.

)

Any chance of running without them? Or is there a cost effective alternative?

Again, thank you very much for any assistance.

Tim

tjkj2002 · **Posted:** Tue Feb 23, 2016 11:19 pm

trivet wrote:

Thank you - that makes sense. I didn't even think the cat might be bad, not the sensor.

And I have 130,000 miles on the Jeep, so I'm way out of warranty unfortunately.

What options do I have? Replacing 1 or both cats will be prohibitively expensive - (a quick Google search shows that this will be VERY expensive.

)

Any chance of running without them? Or is there a cost effective alternative?

Again, thank you very much for any assistance.

Tim

The code description for P0420 is catalyst efficiency below threshold bank 1,it has a sister code P0430 for the same but bank 2.

20 years ASE master tech and only 1 time have I encountered P0420/P0430 and not be a bad cat(s).And yes you must have them and installing the OEM ones,while the most expensive,is the best way to fix it and be legal,plus the engine will not run right without them and that pesky MIL will always be on if you delete them.

toy4everyseason · **Posted:** Wed Feb 24, 2016 3:28 am

Not sure about the space around the O2 sensor but you may be able to run a bored out spark plug anti-fouler between the pipe & O2 sensor. This is how people run cat-less and not throw a code. It is illegal to run without cats or punched out cats and may not work at all if your cat is clogged. You can try some cat cleaner but I really don't think they work. Sounds like the misfire dumped too much fuel into the car and burned it out.

trivet · **Posted:** Wed Feb 24, 2016 11:52 am

Ok- I’ve learned a lot in the last 2 days – thank you.
I also found some really good information about P0420/0430 fault codes here:
https://www.discountconverter.com/catal ... -&News=120

From the site:

- Look at Long Term Fuel Trims (LTFT). These show the amount (in %) the computer is modifying fuel delivery, based on the 02 sensor feedback. Positive numbers indicate the computer is adding fuel, negative numbers indicate the com¬puter is removing fuel. Large positive numbers (>10%) should be investigated further as they indicate the computer is adding more fuel than originally designed.

I don’t have a LTFT, but I do have a STFT (SHORT Term Fuel Trim?) on my code reader– Both banks sensor 2 show 99%. I’m assuming this is not good.

So – where to look next? Suggestions from the site are:

• Bad or Lazy (80,000 + Miles) Upstream O2 Sensor
• Leaking Injectors
• Bad Temperature Sensors
• Bad Mass Air Flow Sensor
• Miss Fire (Coil Packs)
• Bad or Old Spark Plugs
• Clogged Air Filter

Air filter is fine
Spark plugs are less than a year old – but could they have been fouled when I flooded my ignition modules?

Any suggestions on where to look first? It may be that I need a new cat, but I would hate to replace it to just ruin it due to another issue.

Edit to add: The jeep runs very well, no misfires, smooth, consistent idle, no issues at all. MPG is HORRIBLE - I average about 15-16 miles, and it's mostly highway driving to and from work.

Thanks again for all of your help, I have already learned a lot!!

tjkj2002 · **Posted:** Thu Feb 25, 2016 12:33 am

trivet wrote:

Ok- I’ve learned a lot in the last 2 days – thank you.
I also found some really good information about P0420/0430 fault codes here:
https://www.discountconverter.com/catal ... -&News=120

From the site:

- Look at Long Term Fuel Trims (LTFT). These show the amount (in %) the computer is modifying fuel delivery, based on the 02 sensor feedback. Positive numbers indicate the computer is adding fuel, negative numbers indicate the com¬puter is removing fuel. Large positive numbers (>10%) should be investigated further as they indicate the computer is adding more fuel than originally designed.

I don’t have a LTFT, but I do have a STFT (SHORT Term Fuel Trim?) on my code reader– Both banks sensor 2 show 99%. I’m assuming this is not good.

So – where to look next? Suggestions from the site are:

• Bad or Lazy (80,000 + Miles) Upstream O2 Sensor
• Leaking Injectors
• Bad Temperature Sensors
• Bad Mass Air Flow Sensor
• Miss Fire (Coil Packs)
• Bad or Old Spark Plugs
• Clogged Air Filter

Air filter is fine
Spark plugs are less than a year old – but could they have been fouled when I flooded my ignition modules?

Any suggestions on where to look first? It may be that I need a new cat, but I would hate to replace it to just ruin it due to another issue.

Edit to add: The jeep runs very well, no misfires, smooth, consistent idle, no issues at all. MPG is HORRIBLE - I average about 15-16 miles, and it's mostly highway driving to and from work.

Thanks again for all of your help, I have already learned a lot!!

Totally forget about LTFT or STFT when dealing with P0420 code.

You need to look at the B1S1/B1S2 and B2S1/B2S2 readings,if the downstream (B1S2/B2S2) are following the upstream(B1S1/B2S1) the cat(s) are bad and not working thus the P0420(and/or P0430) codes.You need to just look at those 4 O2 sensor readings without any other live data being monitored to get a true look at how they are switching,monitoring other live data with those will slow down the scanner response time unless your using a high end scanner.Those P0420/P0430 codes only deal with the downstream O2's which do not effect mpg's at all,they are there to monitor the cat(s) performance.

Lower mpg's for highway could be clogged cats.

trivet · **Posted:** Thu Feb 25, 2016 9:29 am

Quote:

You need to look at the B1S1/B1S2 and B2S1/B2S2 readings,if the downstream (B1S2/B2S2) are following the upstream(B1S1/B2S1) the cat(s) are bad and not working thus the P0420(and/or P0430) codes.You need to just look at those 4 O2 sensor readings without any other live data being monitored to get a true look at how they are switching,monitoring other live data with those will slow down the scanner response time unless your using a high end scanner.Those P0420/P0430 codes only deal with the downstream O2's which do not effect mpg's at all,they are there to monitor the cat(s) performance.

Lower mpg's for highway could be clogged cats.

I'm agreeing that the cat(s) are probably bad, but my concern is "why"? Are the cats shot because they are 6 years old with 130k miles, or because I have another issue? 6 years seems pretty early for cats to go bad - but 130k miles, maybe not.

It's going to cost a small fortune to replace the cats, so I am very concerned about not finding the cause of the issue.

Any suggestions?

And again, I can't tell you how much I appreciate all of the help I've received from this site.

tjkj2002 · **Posted:** Thu Feb 25, 2016 10:09 am

Higher mileage is a factor for cat's,there average lifespan is 8 years or 100,000 miles and hence the federal warranty set at 8 years or 100,000 miles.Aftermarket cat's will not last as long as OEM cat's and only are 33%-66% as efficient(why they are almost never 50 state legal).

Yes other factors can reduce the life of the cat's but you'd be aware of those issues pretty quickly like a flashing MIL for a severe misfire.Flashing MIL equals "you are doing damage to your cat's right now" type of deal.Over using fuel system cleaners will also reduce the cat's life,there is plenty of cleaners already if the good gas(name brand stations like mobile,shell,conoco and such) that you should never need to add a cleaner but maybe once a year or have a fuel induction system cleaning done more then once a year.To much will damage cat's,also using the wrong types of cleaners and cheap gas also reduce the life of the cat's.

trivet · **Posted:** Thu Feb 25, 2016 10:38 am

tjkj2002 wrote:

Higher mileage is a factor for cat's,there average lifespan is 8 years or 100,000 miles and hence the federal warranty set at 8 years or 100,000 miles.Aftermarket cat's will not last as long as OEM cat's and only are 33%-66% as efficient(why they are almost never 50 state legal).

Yes other factors can reduce the life of the cat's but you'd be aware of those issues pretty quickly like a flashing MIL for a severe misfire.Flashing MIL equals "you are doing damage to your cat's right now" type of deal.Over using fuel system cleaners will also reduce the cat's life,there is plenty of cleaners already if the good gas(name brand stations like mobile,shell,conoco and such) that you should never need to add a cleaner but maybe once a year or have a fuel induction system cleaning done more then once a year.To much will damage cat's,also using the wrong types of cleaners and cheap gas also reduce the life of the cat's.

Ok - looks like I need new cats. Now the search for a "reasonable" price begins....any suggestions? Are there no decent aftermarket systems? OEM is out of the question due to price. The set from here:
https://www.discountconverter.com/direc ... tID=508590
is reasonably priced - no idea if it's good quality or not. Plus I still have to have it installed.

trivet · **Posted:** Thu Feb 25, 2016 1:22 pm

After some Google searching – I’ve found several options. I know nothing about catalytic converters, so opinions/comments/reviews/smartass remarks are all welcome.

Rock Auto – Eastern Catalytic
https://www.rockauto.com/en/moreinfo.ph ... 5139&jsn=8

CarID – DEC
http://www.carid.com/2010-jeep-liberty- ... 5B%5D=1200

Andys Auto Sport – multiple “universal” converters
http://www.andysautosport.com/hi_flow_c ... berty.html

What about MagnaFlow converters? I’ve heard good things about them, and they are certainly reasonably priced.
http://shop.advanceautoparts.com/web/Pa ... rom=header

Hopefully the MagnaFlow converters would work, as I can actually afford these.

As for the Jeep, it’s my daily driver, I average about 20-25k miles annually, mainly highway. No off-roading, the only time 4WD is used is for weather conditions (which is most of the winter here in Michigan :wink:

) It’s more Mall Crawler than Rock Crawler. :roll:

I’m more interested in better mileage and vehicle longevity than off-road performance.

I am not very familiar with newer vehicles, as I am usually working on my 87 GT or 1990 DSM. Much easier to work on myself – and both are catless.

This is the newest vehicle I’ve owned in many years…….so again, I can’t thank you enough for any and all help.

toy4everyseason · **Posted:** Fri Feb 26, 2016 2:46 pm

The ones from rockauto look like a good option & aren't insanely expensive. Of course they won't have the life expectancy of OEM

Scar0 · **Posted:** Sat Feb 27, 2016 4:33 am

A new rear O2 Sensor along with an older front O2 Sensor may cause the P0420 to set.
Just sayen.

trivet · **Posted:** Mon Feb 29, 2016 12:10 pm

Scar0 wrote:

A new rear O2 Sensor along with an older front O2 Sensor may cause the P0420 to set.
Just sayen.

Excellent point. I'll check this out before I order a new catalytic system.

As for a a new system, unless someone can give me a good reason, I'm going to order the setup from Rock Auto. Seems like a good price, shipping is reasonable, and I have a shop that can do the install for a good price as well.
Rock Auto – Eastern Catalytic
https://www.rockauto.com/en/moreinfo.ph ... 5139&jsn=8
As is turns out - this is the exact same unit (didn't notice that right away)
CarID – DEC
http://www.carid.com/2010-jeep-liberty- ... 5B%5D=1200

The online reviews all look good - so I'm heavily leaning towards this one. Should I bite the bullet and order 4 new o2 sensors as well? Or at least the 2 that weren't recently replaced?

Check Engine light frustration

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