Hey guys! First post here, and sadly is for a problem ive been having with my 2006 IS350, first: i got 2 Codes

P0430 Catalyst System Efficiency Below Threshold (bank 2)
P0137 Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)

we thought it was a random code because a week before the code pop up, i switch my Midpipe invidia back to the stock one, so we erased it, then it came back a day later.. we decided to switch sensors from side to side so we can now if it was the o2 sensors or the cats going bad.. after that the CEL came back with 2 different codes

P0420 Catalyst System Efficiency Below Threshold (bank 1)
P0157 Oxygen Sensor Circuit Low Voltage (Bank 2 Sensor 2)

so everything changed sides, so at this point i was sure it was the o2 sensor, i ordered it, it came we replaced it with the o2 Sensor throwing the low voltage Code Friday morning, Check Engine light came back on at night of the same day but this time it was just P0420, thinking it was a phantom code i cleared it (Wishing to be the last time), and for my surprise? CEL again Saturday night and im here typing this cause i dont know what else to do, if anyone could throw some help at me.

Im not refusing to get its a bad cat, but why if its bad, the code would switch sides with the sensors? and apparently is just one of them going bad.. but i dont know what else could be..

i have techstream and checking the live data and some values there

O2S Impendance B2S1: was like 260-300
O2S Impendance B2S2: around 130-170

i guess this have to mean something..

maybe the Circuit of the connector? should i switch sides again to see if the code switch side? a leak? what it could be?

 

Classic exhaust leak symptoms.

 

maybe but where? I went to the exhaust shop this monday, and my axle back had a huge leak, but it was in the back, i dont think that would trigger the code, anyways i fixed it, and today the code came up again, im thinking its where the o2 sensors bolts on, its where is leaking, that would explain the change of codes from side to side.. the exhaust guy told me everything was fine, im telling him to over check the o2 sensors and where the midpipe connects to the cats

 

leaks dont have to be your exhaust. could be your intake not sitting tight, or your intake manifold, or a gasket/seal. its hard to tell without going through the whole system and checking (intake, MAF, throttle body, intake manifold, headers, down pipe, cat, axel and then you also have to check if the sensors are bad)

 

okay i'll check on that, meanwhile, i ordered a O2 Spacer, i checked the cats temp with techstream and theyre all in the same temp.. so i highly think that the cats are not working, the sensors are good, i will clean the maf, and check everything else

 

Those won't cause P0420 and P0430. The catalyst efficiency DTCs happen because an exhaust leak upstream of the catalytic converters divert hot gasses which don't pass through the cats, causing them to warm up more slowly. The catalyst efficiency test is run about 10 minutes into the drive cycle, when the engine has just reached operating temp. Normally, the cats should have lit off by that time, but in the presence of a leak they often haven't.

 

Lets think about this for a moment.. Initially you had:
P0430 Catalyst System Efficiency Below Threshold (bank 2)
P0137 Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)

After swapping the O2 sensors between both sides you got:
P0420 Catalyst System Efficiency Below Threshold (bank 1)
P0157 Oxygen Sensor Circuit Low Voltage (Bank 2 Sensor 2)

This would tell me that your O2 sensor on one side was bad, replacing it was the right thing to do.
However, it looks like your other sensor, while it looks good, is somehow leaking? That's my guess on the matter.

 

Exactly my thought, after the switch, i replaced the sensor that was triggering the p0420 and p0157,but the p0420 reappear, i dont know if its a bad plugged in o2 sensor

 

If you have access to a smoke machine plug one side of the exhaust and fill the system with smoke. If you have a leak you'll see smoke coming out of the hole. If you're certain you do not have any leaks, let me know. I can walk you through a definitive test you can perform to determine if your catalytic converter, air fuel sensors, and oxygen sensors are working properly. That's assuming you have access to a Techstream... I believe I read you did. Correct me if I am wrong.

 

i dont think i have access to smoke machine, but yea youre correct, i have techstream.. i dont know how the exhaust shop check for leaks, apparently they just eye ball it.. where the pipes connect to each other i guess, tomorrow ill go and tell them to check further, to be sure there is no leaks, in fact i have a picture of the cats temp on techstream

Cats temp, the car was running at the right temp, it was not cold
something worths mentioning is that if i cleared the code, it only comes back when i get into a avenue, i mean if the car goes up to 70-100kmh constant, in a 2 or 3mins drive the cel pop up, but if i drive between streets, redlight and traffic, it doesnt.. super weird, i notice this because to go to college a have to get in those speeds, the 2 days i dont have go i am cel free, the moment i start climbing up in speed, the cel appear on me!

 

Update!!

Right now at the muffler shop, the joints where the midpipe connects to the cats were leaking, my mechanic couldnt notice it cause you had to put your hands between the pipe and the aluminum protector thing! Anyways right now my car is waiting to be fix and forget this past 3 weeks with the horrible CEL, ill keep u guys updated

 

Hi
Can you post your updated experience?
Thanks