engine light is on trouble shooting code p0420.


Asked by May 13, 2013 at 08:55 PM about the 2004 Dodge Ram 1500 SLT Quad Cab SB

Question type: Maintenance & Repair

engine light is on trouble shooting code p0420. i replaced 2  of the o2 sensors before
the cat on each side (was told that was bank 1) check engine light is still on........
what else can i check before i replace expensive cats. according to print out it says
possible oil coming out but when i replaced to o2 sensors i pulled out the whole
exhaust and no signs of wetness!!
thanks in advance for the help

3 Answers


4.7 engine!!

3 of 3 people found this helpful.

P0420 catalyst system below efficiency....you know could just be a worn to a stub 02 sensor....surprisingly they wear away as if sandpaper had gotten them...can check to see how many 02 sensors are on your exhaust/manifold now if you'd like~...alas you've already replaced them...the brains of the system would be the ECM and it needs to see the sensors...all of them, your ambient air temp, coolant temp and even envrionmental temp (okay that isn't responsible for bad performance but wouldn't hurt to have a new one) an overfilled gas tank is going to give you a CEL too and takes a couple of tanks full...stopping at the first click please to get it to clear itself~....if you are getting an evaporative CEL~

4 of 4 people found this helpful.

i had a po420 code which is low catalyst i replaced the o2 sensors and the light was still on i want to ebay ordered a new direct fit cat for the left side for less than 200 dollars and replaced it and the light went off and has not come back on yet that was 3 months ago

4 of 4 people found this helpful.

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