ok i have a 1999 5.9l 4speed auto durango the problem ive been having is after driving on the freeway/highway for a while my cel light comes on scanned it and it came up with a p0420 code catatlist effencey low bank 1 so i replaced the front o2 sensor erased the code and no issues till i get on the freeway/highway and it came on again did this 3 times thinking maybe bad o2 sensors but i dont think thats the issue on it anymore i cleaned the throttle body ran fuel injector cleaner threw it cat is fine no issues with it but im out of ideas on it it still runs fine and not going to run similators on it only thing i can think of is that a injector may be leaking and over working the 02 sensor but im at a loss and hoping somebody else may have a idea

 

you replaced the wrong 02 sensor, a catalytic efficiency problem is either a bad cat or a bad POST CAT (Rear) o2 sensor (it could be a wiring issue, but these are very uncommon, 99% of the time its one of the first 2 and 90% of the time id say its the sensor)

 

replaced the wrong sensor ?? it was saying bank 1 which would be the leading sensor right the rear sensor should be bank 2 or are these opposite

 

If you have a catalytic converter code showing up it is either the cat or the post cat o2 sensor since all the post cat O2 sensor does is monitor the catalytic converter function. The precat O2 sensors monitor air/fuel mixture.

 

Symptom:
P-0420 CATALYST 1/1 EFFICIENCY FAILURE
When Monitored and Set Condition:
P-0420 CATALYST 1/1 EFFICIENCY FAILURE
When Monitored: After engine warm up to 147 deg F, 180 seconds of open throttle
operation, at a speed > 20 mph, with the engine at 1200-1700 rpm and MAP vacuum
between 15.0 and 21.0 HG.
Set Condition: As catalyst efficiency deteriorates, the switch rate of the downstream O2
sensor approaches that of the upstream O2 sensor. If at any point during the test the
switch ratio reaches a predetermined value a counter is incremented by one.
POSSIBLE CAUSES
EXHAUST LEAK
ENGINE MECHANICAL PROBLEM
CATALYTIC CONVERTER DEFECTIVE
UPSTREAM O2 SENSOR OLDER THAN DOWNSTREAM O2 SENSOR

 

bank 1 is drivers side not front or back

 

shrpshtr325 ok on the exhaust thou with only 2 sensors bank 1 front bank 2 rear but on the engine it self yes you would be right..

and master tech the front one is newer then the back so thats not a issue. no exhaust leaks that i can either hear nor see and the cat seems fine the exhaust shop checked it out and they said it was fine so id like to think that was out of the picture but i might try replacing the rear sensor and see what happens when i do but was told to also look at the fuel system thought of possibly a leaky injector but thanks for all the replys

 

The o2 sensor can work both ways, If the upsteam is newer that the downsteam. I would replace the downsteam.

 

bank 1 sensor 1 would be drivers side pre-cat
bank 1 sensor 2 would be drivers side post-cat,
bank 2 sensor 1 would be passenger side pre-cat
bank 2 sensor 2 would be passenger side post-cat,

on a california emissions vehicle

a 48 state emissions vehicle will only have 2 sensors so one bank with 2 sensors

and cat efficiency is always related to post cat sensors

 

Correct!

Also, are you replacing your sensors with Mopar sensors and not the standard issue Bosch O2 sensor from Advanced or Autozone? These rigs are famous for giving a code for a bad oxygen sensor even if it's a brand new one.

Get a Mopar one from your parts department at your dealership or get a Denso off the internet. Both will run about the same price.