Acura MDX SUV Forums banner

o2 sensor bank 2 sensor 2 replacement

62K views 27 replies 5 participants last post by  Bratcop 
#1 ·
need help locating the 02 sensor bank 2 sensor 2. i have an 03 mdx that is getting error code p0056. the part was not much so figured would replace myself however i am having troubles locating this part. please help!?!?
 
#2 ·
The bank of cylinders nearest the radiator should be bank 2, since it's cylinders 4,5, and 6. It has two o2 sensors, one in top of exhaust manifold (upstream) and one after the cat in that manifold(downstream). The downstream should be the one you want.

Sent from my XT1585 using Tapatalk
 
#6 ·
FYI, the downstream (post-catalytic converter) sensor monitors the performance of the cat, and that error code COULD be pointing to a bad catalytic converter. OTOH, it's quite common for the O2 sensors to fail after 100,000 miles, and they're a LOT cheaper than a new cat, so it almost always makes sense to replace the sensor first when your car is throwing a code for a secondary / downstream O2 sensor.

And FWIW, it's also possible to install a spacer between the cat and the sensor to fool the sensor into thinking a questionable cat is working properly (by taking the "nose" of the sensor out of the exhaust flow so it doesn't sense as much unburned hydrocarbons getting through the cat). Something like this (not sure this one fits our MDX, but it's easy to find one that does)... CEL "Check Engine Light" Eliminator Adapters

Of course, this is for diagnostics only, and leaving it on your car - even if it allows you to pass emissions testing and turn off your CEL without any negative performance issues - will obviously cause the planet to burst into flames and end all life as we know it within minutes. ;-)
 
#9 ·
Bratcop (as always) makes a good point - a physically bad cat (one that is causing exhaust backpressure) is not going to be "fixed" by spacing out the O2 sensor, even if it turns off the CEL. FWIW, you can often smack the cat (when it's cool, of course) with your hand and hear it rattle if the internals are coming apart. Had it happen in my Jeep, but never anything else (yet...).
 
#10 · (Edited)
Good morning guys,

I currently have error code P0157 on my 2004 MDX and my mechanic keeps insisting that I need to replace the CAT converter but the code is just pointing at the o2 sensor needing to be replaced on bank 2 sensor 2 due to low voltage. I am under the impression that the mechanic wants to rip me off by working on something that might not need a fix at all. I am contemplating on DIY but have no idea if it is a simple thing to do.

My MDX has 173K miles btw.

Please share your thoughts on what I should do.

Thanks,
 
#12 ·
O2 sensors report a voltage to the ecu typically 0 to 1 volt. Different voltages are interpreted as different fuel mixtures. The downstream sensor is used to monitor the cat function. The upstream sensor is used to monitor mixture. If upstream sensor says mixture is fine and downstream is out of whack, it close be 02 or cat. 02 is easy cheaper, try replacing it. If it didn't fix the cel, then it's cat. I replaced one cat, it's not that bad, I think under 200 bucks for the part.

Sent from my XT1585 using Tapatalk
 
#13 ·
Play the odds and replace the O2 sensor. They're MUCH more likely to fail than the cat, and unless your cat is rattling (as when the internals break down), or your mechanic put a sniffer on the exhaust to diagnose it (doubtful), you're 90% likely to fix the problem with a new O2 sensor. If you still get a CEL after replacing the O2 sensor, some folks will just put a spacer under their O2 sensor, which takes it mostly out of the exhaust flow, and will clear up the CEL (and allow you to pass inspection). This won't "fix" a clogged up cat, but if your cat is contaminated from some sort of event (like a bad tank of gas) then this will take care of it.

I should mention that there are other things that can cause a P0157 code, like bad wiring or a defective PCM. There are ways to troubleshoot that, but O2 sensors are always suspect after 100,000 miles or so, so I'd suggest just swapping that sensor out and consider it preventative maintenance if it doesn't fix the issue.
 
#14 ·
Thanks for the suggestions! My mechanic quoted me upwards of $1,000 for replacing the CAT and the oxygen sensors but now I see that I can get the CAT for 200 more or less which reassures me that he just wants to break my bank. I will replace the o2 sensor over the weekend and let you guys know if the CEL goes away.

Is the CAT converter an easy job to do also? Just looking at the part looks like an easy plug and play type of situation but I am inexperienced and worried that it might be quite a hassle to replace.
 
#15 · (Edited)
Good morning guys,

so I changed the o2 sensor on saturday and the code went away but new codes came out on the following day :(. Now I have codes P0300, P0301, P0302, etc... and code P0420. I did a valve adjustment on my vehicle a couple of months ago so I am taking it in to see if the valves got tight once again given that I have warranty on the valve adjustment for a year. My question is, does the CAT have anything to do with the valve adjustments? I am under the impression that my rear CAT might be tightening my valves but I want to confirm before I take it in to the dealer and have the valves adjusted once again along with replacing my CAT which they will take an arm and leg off from my body most likely.
 
#16 ·
Catalytic converter does nothing but syphon off/burn harmful gases before they get out your tailpipe. Valves tighten I believe because of wear in the valve seats after tens of thousands of miles, should not be anything that can happen after u just had them adjusted. Upstream 02 sensor measures gases and tells engine computer to enrich or lean out fuel mixture which it does by controlling injector pulse width mostly. Downstream o2 simply tells computer if catalytic converter is working correctly, which I think it does by comparing it's value to that of the upstream o2 sensor for that bank. None of the o2 or cats affects valve tightening or adjustment

Sent from my XT1585 using Tapatalk
 
#18 ·
I was thinking maybe the cat was breaking apart internally, and that the resulting back pressure was causing misfires. That could be consistent with the codes you're getting now IF you are only getting P0301 through P0303, which would indicate misfires on cylinders 1-3 (plus the random misfire code, which would be normal in that situation). Your post was a little vague about exactly which misfire codes you're getting. But if a new O2 sensor is reporting there's still a problem, AND you're getting misfires on just that bank, my money's on the cat itself being bad. Give it a good thump with your fist and see if you hear anything rattling around loose inside.
 
#19 ·
Vehicle's currently at the dealer getting serviced. I have not received any calls yet regarding the issues but I was told that the either engine might have some damage, fuel injectors might have gone bad or it could be something as simple as a coil. All codes were P0300, 0301, 0302, 0303, 0304, 0305, 0306 and P0420. Since I had the valves adjusted in July, I still have warranty and it is the reason why I took it in. Should I replace the cat with them or just order the part and get it done elsewhere? I don't want to break my bank with them but I do want that CEL gone for good and mileage improvement as my vehicle is currently giving me 12.5 MPG instead of the 17 MPG that I should be getting.

I really appreciate your help habbyguy and bratcop!
 
#20 ·
12.5 is abysmal, I don't think all injectors or coils would fail at the same time. When was timing belt changed? Check the timing, maybe it jumped? If be curious to know what the ltft and stft values are, that can tell you a lot about what's going on. Compression test is anyways good starting point as well

Sent from my XT1585 using Tapatalk
 
#21 ·
Ltft =long term fuel trim=cumulative numeric value of quantity of gas added or subtracted by computer to get proper mixture. If o2 are failing, engine will dump way too much fuel or not enough causing misfires, etc because it thinks it needs to. Had a bad o2 on f150 that was failing but not throwing a code, caused multiple random misses and rough running (which did set codes), I caught it by watching voltage values for that o2 live to see it jump like crazy and computer pour in excessive fuel causing misfires.
Bratcop
P.S. Id rather spend any necessary money on tools and parts to replace the cats myself then fork out excessive money for them to do it.... My .02, or find someone else to do the exhaust work, got to be cheaper
Carry on and fear not the DIY

Sent from my XT1585 using Tapatalk
 
#22 ·
I agree with Bratcop - always better to spend money on tools and equipment, rather than giving it to a dealer / repair shop (where possible, that is).

FWIW, I always buy one of the clones of the dealership diagnostic software / hardware for my cars, figuring the first time I use them, I've paid for them (and I've helped a lot of buddies with similar cars out). The HDS (Honda Diagnostic System) clone can save you a lot of time and give you a lot of information, but can also be "interesting" to get working the first time, even if you're pretty good with a PC. A much easier and less expensive tool that is REALLY helpful if you have a droid style phone is the Torque app. I think it costs $5-10, and the bluetooth OBD dongle that it works with can be had for well under $20. With that, you can custom-design a "dashboard" of gauges for your vehicle and monitor all kinds of systems, including the O2 sensor outputs (in graph form if you like), fuel flow, temperatures, readiness status (handy for a self pre-check before inspection), etc., etc., etc. There are similar apps for other phones (windows phones or iphones) but I'm not as familiar with them, and the associated hardware for the iphone is a lot more expensive (of course). ;-)

I think the timing is as good a place to start as any - a bad cat should only affect one bank of cylinders (though it could cause horrible gas mileage). Hard to imagine two cats going bad unless something really traumatic happened (like someone ran a lot of leaded fuel through the car... hard to imagine these days).
 
#24 ·
Long story short, dealer is saying that all sorts of codes are now coming up and they are showing gas too lean. She claims that it might be the sensor that I replace which was aftermarket and could be crappy (NGK o2 sensor for bank 1, sensor 2). She said the CAT definitely needs to be replaced so I asked her to send me a quote on how much it would cost me to replace the CAT and that one sensor. Do you guys where I can buy a reliable CAT converter for bank 1? I am contemplating taking my vehicle back and looking for another shop to replace my CAT. She also claimed that my brake pedal is too low because I have crappy aftermarket rotors and pads. Fronts are also shot and I am thinking about getting aftermarket lower arm controls and end links (moog brand) to replace along with KYB struts.

She also said that the rear main seal is leaking bad and it is expensive to replace, is this true? Please advise as I am going crazy over all this given that it sounds like a ton of cash that I will have to spend.
 
#25 ·
Second opinions are always good, rear main seal is cheap, labor to get to it isn't. I don't think down stream controls rich or lean, just cat function afaik. Not so sure on brakes...I got my cat, a walker, off rock auto.com, under 200

Sent from my XT1585 using Tapatalk
 
#26 ·
You can get a cat and a new O2 sensor from rockauto.com for not much more than $200. And Bratcop is right - the downstream (#2) sensor is only there to monitor the performance of the catalytic converter - it won't affect the air/fuel mixture (that's the job of the upstream (#1) O2 sensor.

I'm at a total loss as to why you'd have a low brake pedal based on replacing rotors and pads, unless the rotors were horribly warped (which would be obvious) or the pads were soft (which I can't imagine under any circumstances). My guess is that there's simply air in the lines - so the dealer would sell you expensive rotors and pads, and then bleed your brakes (only the last step will actually improve anything, I'm betting).

LCAs and links are always a good idea, if your old ones are shot.

None of this is expensive unless you take it to a dealer. If you're a fairly competent DIY type, it's almost cheap (probably $500 for the everything you're considering, other than front struts).
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top