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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!?!?
 

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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.

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Run the vehicle until the exhaust is hot. Then put on some gloves so u dont burn your hands and take it out. The heat makes it easier to get out.

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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. ;-)
 

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I've bursted the planet into flames many a time and ended all life before so I can say without reservation, heed the Habbyguy, but fear not the DIY! Lol

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But on point, that cat was bad on mine, internals were all broken up and falling out so I replaced it

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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...).
 

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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,
 

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At that mileage you can't go wrong by replacing the downstream sensor as a maintenance item. The worst case is needing to do the catalytic afterwards.
 

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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.

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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.
 

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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.
 

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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.
 

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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

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And if it were me and my daily driver, I'd assume all the o2 were on the edge of reliable and replaced the other 3. Quite a cheap investment that could actually improve your mileage a little.

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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.
 

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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!
 

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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

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