I have code P1038, high voltage to the o2 sensor bank 1, sensor 2. And now I have code P0420, catalyst system efficiency below threshold bank 1

I'm leaning toward both these codes being cause by a bad o2 sensor, post catalytic converter. Ive had P0138 for months, I'm thinking that the computer is thinking the cat is dead because the readings between the two sensors haven't changed in quite some time.

Does that make sense to anyone else, or is my thinking illogical?

Car has 154,000 Kilometers on it. (so just under 100k miles)


My other questions is are you able to just cut out the cat and weld in an aftermarket catalytic converter made by Magnaflow or something, instead of having to buy the entire exhaust manifold / cat assembly. It seems like such a stupid design to have both those parts as one.

 

What year and model car do you have? My S has a separate exhaust manifold and downpipe.

 

just figured i would toss it out there that i have for sale a stock exhaust manifold, cat, and already one-ball modded catback piping with stock tips off of my 03 s with about 60k miles on them. no problems. located in northeast CT if youre interested.

however, it sounds like your o2 sensor/s could be the issue. if you provide the year and model of your vehicle, as well as any modifications, we can help more. there are many threads on here related to problems with o2 sensors.

just know beforehand that if replacing the pre-cat/upstream sensor, you MUST get the NTK brand. the post-cat/downstream sensor can be replaced with Bosch.

if you decide to get a new cat as well, magnaflow does make a high flow model which i had installed on my car. to my knowledge, it can be used with the stock exhaust manifold and back piping. i have a header and aftermarket exhaust installed, so it was necessary for my needs, but its a quality high flow cat for the price in my opinion. ill look up the correct part #'s for each of those pieces for you, and youre interested in my stock exhaust parts, just send me a pm.

 

My apologies, I forgot that information.

Car is a 2005 Cooper S.. I think its a sept or oct 04 build date

 

I have stock header/cat --> stock pipe size ---> back to what looks like an aftermarket or a replaced resonator ---> into two smaller sized magnaflow mufflers.

The resonator has a piece broken off inside and it rattles around. it is fairly new so I can only assume it is a cheaper aftermarket piece.

 

Are you sure the cat is bad? Try replacing the sensor only and hopefully that is the main issue.

 

Magnaflow High Flow Cat
Part # 94136


NGK PRE-cat o2 sensor
Part # 25648


Bosch POST-cat o2 sensor
Part # 13878


(i like amazon. usually cheaper than most places and usually free shipping)

again, mine is an 03 s, but as far as i know, they are the same.

 

No, I am not sure if the cat is actually bad. I just wanted to know if people just cut out the old cat and weld in a new one, or if that OEM exhaust manifold / cat is a special assembly that you absolutely need. just seems like a big cash grab to me. I'm not about to replace an exhaust manifold if its not broken..

I'm leaning toward the second O2 sensor being faulty, which is causing both codes.

 

good stuff, thanks. I checked if "it fits" on the amazon site for the cat, and it says it doesn't. How do you know if that particular cat will work with our cars?

 

thats the exact one i purchased. it says it doesnt fit mine as well. i think the reason for that is because it is a universal cat, so it does not have the flanges on both ends. this allows it to either be welded in as is, or, to have flanges welded onto it so it can be bolted to the corresponding parts.

in my case, i had them weld a flange onto the header side, as to keep the header in tact, and then just weld the back side to the back piping.

also, i believe this cat has a 2.5" inlet and outlet, which is a little larger than our stock piping, but that is part of what gives it the high flow properties (aside from the internals of course).

if it doesnt seem right to you, i understand. doesnt hurt to keep browsing if your in the market. that is the exaxt one i have on my 03 s though.

 

I'm sure if it worked on your car, then it should be fine for my car as well.

I'm going to order that second 02 sensor first and try to get that installed myself out in the freezing cold lol. Hopefully that fixes it, if not I'll probably be looking at getting that cat.

 

If I just go ahead and change out the o2 sensor myself, will the CEL go away on its own if the new sensor fixes the problem ?

 

The CEL just needs to be cleared, if you don't have the ability to clear it just go to Autozone or Discount auto parts they can clear the code for you for free. If the problem was your sensor the CEL wont reappear.

 

ok thanks, we dont have autozones here and i'll likely have to pay some shop to clear the code.. may as well have them replace the o2 sensor if thats the case

 

or... what tool do i need to be able to reset the lights myself. ?

 

http://www.ebay.com/itm/New-Autel-MS309-OBD2-OBDII-Scanner-CAN-BUS-Car-Code-Reader-Data-Tester-Scan-Tool/121261175461?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D261%26meid%3D4374804048930918900%26pid%3D100005%26prg%3D1088%26rk%3D2%26rkt%3D5%26sd%3D191049833984%26

would this work?

 

get a scanguage2. and tools to replave an o2 sensor include some pb blaster, and/or an o2 socket/wrench. maybe a torch if its super rusted. theres gotta be somehwere that can clear the code for you though.

 

No, I've been through this before. No one will do it for free.. If that cheap code reader wont do the job I may as well just save myself the time and have a shop install the o2 sensor and clear the codes for me. I'm trying to fix this problem on a budget.

 

I don't see why this cheap-o version won't do the trick.

 

I bought a $20 one off of Amazon and it works fine for Pulling codes and resetting them.

 

Mission Complete. swapped out the second o2 sensor and cleared the codes. engine light is off and has stayed off for 100+km Need to wait until the ECU completes 3 cycles and at least 200km of driving until I am allowed to etest it.