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Lori 05-16-2012 08:52 PM

CEL Trouble
Hello All,

I just purchased my used 2007 Jeep Patriot last Saturday, May 5th, since then it has been to the shop 2 times to replace the intake manifold runner (it was broken and stuck open), and also the catalytic converter was replaced as well. The Check Engine Light came on after the cat was replaced with an O2 Sensor low efficency code. I replaced the O2 Sensor and the CEL went off. A few days after the O2 Sensor was replaced and the light had gone off, the CEL came back on again for the SAME O2 Sensor reading the same low efficency code P0420. A mechanic friend of mine suggested it might be the fuel injectors leaking or that the fuel/air ratio might be running rich. Any suggestions on how to fix the problem? Or has anyone come across this problem before?

Also I should add my Jeep has 117,000 miles and is a 2.4L.


2005JGC 05-27-2012 02:08 AM

Re: CEL Trouble
did they use a mopar (denso) o2 sensor? anything aftermarket (ESPECIALLY bosch) SUCK and can and WILL throw fault codes. Replace it with a denso o2 sensor and you will likely be ok...

That said you may be dealing with an exhaust leak also.

Your mechanic friend is WAY over thinking this, that is ridiculously uncommon when there are an handful of common causes.

Not sure if your even going to be back around, if you are feel free to follow up here but if you have any questions and want to ensure I will see it in a timely manor feel free to send me a personal message.

Lori 06-01-2012 08:14 AM

Re: CEL Trouble
Thank you for the reply, I replaced the O2 sensor with a Bosch and the light went off for a day and then came back on so I returned the 02 sensor and replaced it with another Bosch thinking the first sensor was bad. The light went off for 3 days and now it is back on with the same code of low efficiency. I will try to get a Mopar O2 sensor and see if that fixes the issue. The Intake Manifold Runner has been replaced in bank one and the catalytic converter as well as the spark plugs, the car seems to be running fine although I am still only getting 25MPG highway.

Also I am wondering if there might be a cross connection with my cruise control as every time the CEL has come on it seems to be when I am cancelling my cruise control? Could that be an issue? I disconnected my battery for about an hour seeing if it might clear the CEL code but, it did not.

2005JGC 06-01-2012 02:57 PM

Re: CEL Trouble
Yes get a mopar sensor in there, you may be supprised with a fuel economy gain with a proper sensor in there considering its your O2 sensors that deturmine how much fuel to give. It also uses O2 sensor operation to deturmine your catalyst effiency, so I wouldnt worry about anything until you have a proper sensor in there... THEN go from there.

Probably more like dumb luck w/ the cruise control, your o2 and catalyst monitors run doing about 55 (plus or minus 10mph or so) with light throttle apply and medium to low load... about the time you would be using your cruise control ;) and typically they are a 2 trip fault iirc so its not going do throw the CEL the first time it runs the monitor, but it will the 2nd.

Lori 06-11-2012 02:32 PM

Re: CEL Trouble
I replaced the O2 sensor this past Saturday with the MOPAR sensor and the CEL immediately went off. :arms: I don't want to jinx, but it seems to be staying off although, so did the other sensors for a few days. I will obviously keep an eye out for it and see what happens but, I thank you for your help.

Lori 09-20-2012 08:33 AM

Re: CEL Trouble
Ever since I replaced the O2 sensor with a MOPAR sensor back in June about every other month the CEL will come on for a few days with a code for the same O2 sensor I replaced stating the fuel mixture is too rich, then after a few days the light will go off without me doing any work to the car. Do you have any advice?

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