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OBD II Code P0420


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4 replies to this topic

#1 oscarcat

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Posted February 28, 2011 at 01:35 pm

This is a post to correct the confusion/error in my previous post regarding my trouble code for 2005 T&C 3.8 liter V-6, 77k miles. New plugs and wires at 75k as recommended under severe service schedule. OBD II scan tool read code P0420. The text said "catalyst system efficiency below threshold bank 1". Vehicle is still under the 8yr/80k mile Federal emission warranty which covers the catalytic converter and the emission control module. With my luck my problem is not covered. So my question is what is involved in changing the O2 sensor[s]? I can see and feel one, haven't gone under the van to look for the second one.

Has anyone changed the sensors on this vehicle? I can feel the one sensor just ahead of the firewall although there are some lines in the way, HVAC I think.

Where is the second sensor?

I have a pair of ramps so can get underneath without difficulty, have a garage etc.

My skill level is spark plugs and sway bar bushings on that vehicle. I am willing to purchase the special O2 socket. Or should I just take it to have the work done because it is such a knuckle buster. ? Dealer quoted in the $300 range to test and replace one O2 sensor assuming that is the problem. I can purchase both O2 sensors from wholesalemopar.com for about $120 and if the job is not extremely complex I'd rather spring for 2 new parts and provide the labor myself even if it only needs one sensor.

What should I know before going with dyi option or dealer service option?

#2 ImperialCrown

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Posted February 28, 2011 at 05:15 pm

When the PCM runs it's emission monitor tests, it's usually pretty accurate in determining which components have failed. The O2 sensors are tested first to make sure that the Cat test outcome will be valid. If you have erased the P0420 code and it came back, it's almost sure not to be a fluke. Unless you have stored O2 sensor or lean/rich fault codes, I would leave them alone and let the dealer handle this one.
There was a TSB # 18-010-05A for a false P0135- upstream (1/1) O2 sensor heater performance faullt code for 3.8L RS built between 7-8-04 and 3-2-05 that involved a PCM software update (also 8/80 although a diagnostic charge would be up to the dealer). See your driver's door sticker for the MDH # (month, day, hour-build date).The latest and greatest software updates are desirable.
A P0420 fault code usually means a catalytic converter replacement.

#3 AllanC

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Posted February 28, 2011 at 09:38 pm

The PCM (powertrain control module) compares the switch rates (lean-rich-lean) between the upstream and downstream oxygen sensor. If the downstream switching rate approaches too closely the upstream sensor switching rate, it assumes the catalyst is loosing effectiveness and sets code P0420. The problem is that the catalytic converter should last 150,000 - 200,000 miles or more. Failure at 75000 miles might mean some unwanted operating condition exists which contaminated and/or ruined the catalyst. You are within the 8/80000 mile warranty so you should be able to get it replaced at no cost to you. However if there is an underlying condition that caused the premature failure, the replacement will fail prematurely on you also.

Maybe paying for a diagnostic test and checking the switching rates of the upstream and downstream sensor is in order. I would suspect that the dealer service department must do that at a minimum to determine that the sensors are functioning properly and the catalytic converter is at fault.

#4 oscarcat

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Posted March 5, 2011 at 10:42 am

This is a post to correct the confusion/error in my previous post regarding my trouble code for 2005 T&C 3.8 liter V-6, 77k miles. New plugs and wires at 75k as recommended under severe service schedule. OBD II scan tool read code P0420. The text said "catalyst system efficiency below threshold bank 1". Vehicle is still under the 8yr/80k mile Federal emission warranty which covers the catalytic converter and the emission control module. With my luck my problem is not covered. So my question is what is involved in changing the O2 sensor[s]? I can see and feel one, haven't gone under the van to look for the second one.

Has anyone changed the sensors on this vehicle? I can feel the one sensor just ahead of the firewall although there are some lines in the way, HVAC I think.

Where is the second sensor?

I have a pair of ramps so can get underneath without difficulty, have a garage etc.

My skill level is spark plugs and sway bar bushings on that vehicle. I am willing to purchase the special O2 socket. Or should I just take it to have the work done because it is such a knuckle buster. ? Dealer quoted in the $300 range to test and replace one O2 sensor assuming that is the problem. I can purchase both O2 sensors from wholesalemopar.com for about $120 and if the job is not extremely complex I'd rather spring for 2 new parts and provide the labor myself even if it only needs one sensor.

What should I know before going with dyi option or dealer service option?


THIS IS MY FOLLOW UP: I TOOK IT TO MY DEALER, THEY DETERMINED THE P0420 CODE WAS THE CATALYTIC CONVERTER, THEY REPLACED IT AT NO COST TO ME UNDER THE FEDERAL 8YR/80 WARRANTY. WAS IN THEIR SHOP OVERNIGHT BECAUSE THEY HAD TO ORDER ONE PIECE OF EXHAUST PIPE [NO CHARGE TO ME] AND IT IS ON THE ROAD AGAIN. GOOD DEALER EXPERIENCE [BOB BAKER CHRYSLER JEEP IN CARLSBAD [SAN DIEGO] CALIFORNIA. THANKS TO THOSE WHO RESPONDED. REGARDS, OSCARCAT.

#5 ImperialCrown

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Posted March 5, 2011 at 11:50 am

I'm glad that it was fixed to your satisfaction and that the light is now out.


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