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o2 sensor/cylinder misfire?

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7 replies to this topic

#1 keviv

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Posted May 4, 2007 at 10:14 am

The check engine light on my 04 T&C went off a week or two ago. The code I pulled was a p0420 -- the downstream o2 sensor. Thinking that this was emissions-related, and if not, should be covered under my extended warranty, I took it down to the dealer this morning.

So the dealer tells me that they're reading a misfire in the bank 6 cylinder. That the unburned fuel is going down the exhaust, and that's affecting the o2 sensor. He recommends getting all 6 plugs and wires replaced (they only have about 29k miles on them), and then obviously swapping out the sensor. He'll cover the sensor under my warranty, but wants $300 for all the plugs and wires replaced.

I have two questions on this situation:

1. I never saw a code for the cylinder misfire. The only code I saw was for the o2 sensor that I mentioned above. Does it sound reasonable to claim that it's the plug/cable, or is he just throwing parts at it rather than properly diagnosing it?

2. I had a major tune-up, which included all new plugs and wires, 29k miles ago (18 months ago...) as I mentioned. My first inclination was to say that I should just have them change the plug and wire on the mis-firing cylinder. The dealer refuses to do this, saying he really would recommend doing all six "for my safety". He won't give me a better answer. Is there any sound reason that I shouldn't replace just the one?

Also, I think cylinder 6 is on the front of the engine, right? How hard is it to reach this plug if I wanted to do it myself?

Thanks guys!


#2 valiant67


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Posted May 4, 2007 at 10:37 am

The plugs and wires (assuming original types were used like Champion Platinums) should be good for 100K miles. Mine certainly were in my 99. If there's a problem in the plugs or wires, I'd say it's poor installation or poor materials.

The rear (or downstream) O2 sensor really does not affect engine performance. That's the job of the upstream O2 sensor. The second sensor monitors the air after the converter to see that it is cleaner than what went into the converter.

#3 Bob Hohn

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Posted May 4, 2007 at 10:58 am

You may want to find out if your T&C falls under the TSB that was issued for that problem. I believe it involves a reflash of the PCM. Buddy of mine had it happen to his '04 and it only had 26,000 miles on it when it happened.

#4 keviv

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Posted May 4, 2007 at 11:06 am

thanks guys.

valiant - yeah, i understand the difference between the two sensors. i'm worried that if it's really a problem with the cylinder and not the sensor, i could blow the cat if i keep driving -- if the sensor is functioning, it's telling me that the cat is not burning enough pollutants. that's why i wanted to get a sense of whether it's possible to see an o2 code and no cylinder misfire code if it really is a cylinder misfire.

bob - thanks, do you have any more details on that recall? i have access to alldata, and i did a quick search. there's a lot of TSBs, and i can't figure out which one you might be thinking of.

thanks again, all. and if anyone has thoughts on my original two questions, i'd appreciate it!


#5 BAJA73

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Posted May 4, 2007 at 02:34 pm

You could pull the plug and see what it looks like.

#6 Bob Hohn

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Posted May 4, 2007 at 02:35 pm

I don't know what the TSB was called, but it had to do with mis-fires and check engine light coming on.

#7 ImaginThat

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Posted May 5, 2007 at 07:32 pm

Try lookin up TSB 18-018-04, it replaces all plugs and plug wires due to wire rubber deteriorating and they flashed comp to newest revision. Mine was done at 26,500.

#8 vwaudifreak

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Posted May 5, 2007 at 07:46 pm

Plugs and wires are covered under the 8/80 federal emmissions warranty. Chrysler will only cover the part that failed, not the entire set. Plugs and wires are considered a "maintenance" item, but when you have one that goes bad and it is causing your emmissions to be beyond the federal limit, Chrysler has to cover it.

Take it back to the dealer and let them cover it under the 8/80.


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