Hi, Ive been having terrible gas mileage recently, ran the OBD and got P0420 Bank 1(new code), I remember some years ago, i showed the mechanic a P0057 Bank 2, Sensor 2(old code), he said to not worry much about it..

So Im going to buy the O2 sensor for the P0420, and figure replace the P0057 as well, but I haven't found any info about the P0057 part, is the HO2S same as the a regular O2 sensor?

Also I read here that its a good idea to replace both sides, found this in Rock Auto, do they have a side or it will fit both sides and just buy 2, is this good?

https://www.rockauto.com/en/moreinfo...&jsn=14&jsn=14

It might be the Cats, but either way I was going to buy both sensors if I had to replace the cats, so i might try sensors first.

Thanks in advance for any help and comments about the part i linked

 

The P0420 code means you need a new passenger side cat. The rear sensor is detecting that the cat isn't doing it's job of cleaning the air. https://www.yourmechanic.com/article...xygen%20sensor

 

You have two different things going on with two different sensors.

P0057 is for the heated circuit within the Bank 2 (Driver-side) O2 sensor, hence the "H" in HO2. This function allows for the sensor to heat up faster. In all likeliness you can ignore this as I am not 100% sure that code alone would set the CEL (idiot light).

P0420 is for the actual O2 sensor for Bank 1 (Passenger-side), specifically, the efficiency of the sensor is below threshold. So, as member "mummy2" suggested, more than likely you need to replace the sensor.

If it were me, I would just replace the passenger-side sensor to resolve the P0420. If the P0057 persists, or sets the CEL then you can replace the driver-side. Unless you just want to knock them both out at the same time, that is your call.

 

Thanks, Im a bit confused, yeah the OBD was giving me the heated circuit, and the other the O2, so i found this one https://www.rockauto.com/en/moreinfo...&jsn=14&jsn=14 is this a good one? but what im confused, is the Heated Circuit part of the O2 sensor? i know the HO2 has been giving CEL for years, like you said the mechanic said to ignore it, but i dont mind changing both sides since im on it and get rid of that light.. do they have a side or just buy 2 of those that i linked for each side?

 

The heater circuit is within the sensor itself. To "fix" the heater (P0057) you have to replace the sensor. Most people will ignore this code as long as the sensor is still functioning normally otherwise.

That said, the link you reference appears to be correct. Stick with Denso or NTK as these are OEM suppliers. There is no "side-by-side" distinction for these sensors so, yes, you can just buy two (2) of the same.

 

Thanks a lot ILM, Ill get them now, they are somewhat cheap compared to other stores on the internet

 

So i Replaced both O2 sensors, cleared the codes, ran the OBD and no erros, not CEL, but i just sarted the car, didnt drive it... driving it this morning to work the CEL again, just got home, ran the OBD and P0057 again, fortunately the P0420 is gone... after replacing it, why I might be seeing this code again?

 

Being that the P0057 is being persistent especially since you replaced the sensor, the issue then points to either a wiring harness issue, a bad ground, or the ECU is not playing nice.

The best advice is go download the EC (Engine Control) section of the factory manual for your car from here. It has a full diagnostic section for the P0057 code including what wires to check, resistance values for the sensor(s), etc.

For the time being I would just ignore it.

 

Looks a bit more complicated than what i was expecting, i think that code can is the reason i have the CEL, its been a few years and thats been the only code, unless something else is not working correctly and OBM doesnt see it…

ill check the link and see if i can figure it out..

Since you mentioned the ECU, i just remembered, i had a code before, its not showing anymore, it was about the ECU, i don’t remember the code, but searching here, you mentioned something about the ECU getting wet because of the rooftop leaking problem.. i had a leak a few years ago, until i replaced the filter, which i have to do it again..

other thing I noticed, is that the gas mileage hasn’t improved, which was my main concern, I thought fixing the P0420 was going to fix it, ill have to give it a couple of days to check the average, but i think nothings changed, could that be because of the P0057?

 

The P0057 is not a performance code in that it should have no effect on your mileage. Possible, if the sensor is not getting hot enough, but not probable. The downstream H02S's measure the performance of the catalyst/ catalytic converter and have no effect on engine performance ,per se. However, the upstream AFR would have a direct impact on engine efficiency, but that is a topic for another time.

The heater function is not active all of the time. As the exhaust gases heat up the sensor this circuit gets turned off by the ECU. That said, if the ECU got wet, then it is entirely possible some of the connections may be corroded/ dirty/ etc. Or, there is a wiring issue between the ECU and HO2S.

If I were you, with the battery disconnected, I would disconnect the harnesses at the ECU and check that the terminals and pins are clean and dry. While disconnected, you can then run continuity tests on the wires going from the ECU to the driver-side HO2S. I would also check that all of the ground connections around/ near the ECU are clean and tight. These ring terminal connections are known to corrode over time.

 

Thanks, ill give it a try to do the diagnostic section for the P0057 first, and probably during the weekend i will do the ECU check, its so hot outside...

Is it possible that the CATS are bad and causing the bad mileage? I read that the spark plugs, the cats and maybe other thing can go bad for driving the car like that, any thoughts on CAT cleaners? i dont know if i trust those things even though i watched some videos helping, also want to clean the MAFS that might also be a reason for the bad mileage..

 

Thanks! so i took it to a couple of mechanics, both codes are still there after replacing the O2 sensors, the first one cleaned the air filters and maf sensors, checked spark plugs and said he didnt see anything weird, i asked him about replacing the cats for HFCs and told him i saw a couple (that were mention here, one was Kinetixracing) that are legal and wont throw CEL code, at least thats what their website says... he said that its a 50/50 and he wont warranty anything... and last weekend took it to another guy, a muffler shop, he said its one of the CATs, he recommended Magnaflow(around $1300), I told him the same i told the other mechanic, that are legal and wont throw codes, he just said bring them ill install them.. does anyone have experience with the Kinetixracing HFCs and know if they really wont throw codes? or any other recommendation about what to do with the CATs thats not so expensive? the Kkinetixracing are around $450 which sounds great..

 

Sorry to keep posting here on and old post nobody has replied, but i hope somebody can guide me, so the mechanic didn't find anything related to the bad gas consumption, I finally got the cats replaced, but that didnt help, he did find a short in the harness and i finally got no codes anymore... what else can be the problem, ive been having some high and rough idle, i cleaned the throttle bodies but they weren't too dirty, almost clean, i did the pedal, valve and idle relearn but same rough and high idle...

Can the throttle bodies cause the high mileage, how can you tell if they are bad? some posts here stated that the rough idle was only fixed after replacing them... what else can be causing this bad mileage?

Thanks...