Hi all, first timer here. I havea P0135 code saying O2 Sensor Heater Circuit Malfunction, Bank 1 Sensor 1 on my 96 civic. Is it necessary to disconnect and take voltage readings to confirm the O2 senor is bad or is it a no brainer to just replace? Are there available directions for how to do these tests? Also, isBank 1 Sensor 1 thetop one located in the exhaust manifold or is the onebelow the cat?I was poking aroundand removed the heat shield to look at thetop sensor and noticed what appears to be a crack in the manifold, but not sure how deep.Might this be the problem? Would welcome any help on this, thanks!

 

i assume you've got a DX/LX, and the crack runs right through the O2 sensor?

 

Yesits a DX. I need to look again,but I believe the crackisjust aft of the sensor,with the crack running in thefront to back direction. As I never took the heat shield off before I'm not sure how long it hasbeen like that.

 

sort of like this:



O2 sensor hole is on left

 

That looks a lot like it. Does that require a new manifold?

 

generally yes, depending on how bad the crack is, it might be weldable, but that requires taking the header off anyway

car will still run, with good o2 sensors it won't throw a check engine light, but you will notice noise & decreased gas mileage, as it's an exhaust leak pre-catalytic converter, so the second o2 sensor thinks the car is running ridiculously lean, so it over compensates...

i ran mine like that for about 2 months with knowledge of the crack, then replaced the entire exhaust system.

it's an odd part, dealer wants around $650 for a new one, plus installation, magnaflow makes a direct fit for around $580, and there's a couple other new manufacturers for them, but it's still pretty much, you have to replace the header/catalytic converter assembly. not that hard of a job to do, but it's worth upgrading to the EX style exhaust system (this would require a EX header/downpipe, new catalytic converter, and EX mid pipes, you could keep your muffler)

I replaced my whole system with megan racing header, magnaflow high flow catalytic converter, and a RS*R exmag exhaust for around $950 after buying a new O2 sensor to replace my downstream one, then installed it myself in about 5 hours.

as to the original question:

I think bank 1 is the upstream sensor. the crack is kind of secondary to the sensor...

 

Thanks a lot for taking the time torespond. Sounds like if I take it to a shop we're talking over $1500.It doesn't seem unusuallyloudso I'm guessing its not cracked through although I suppposeI could remove the heat shield and run it to get a better senseif it is. I think I'm just going to try replacing the sensor fornow. I wonder if a high temperature epoxy would work to fill the crack?

 

total, installed, a shop told me around $900 or so...

it's about a 2 hour job depending on how rusted the bolts are holding it in place, and pretty easy to do if you're so inclined... If I can find some free time, I'll finish my write up for doing the swap

 

Back again. I replaced the upstream O2 sensor, the engine light goes off and the car is running better from the standpoint that it doesn't feel like its about to stall at every stop light. A day or so later CELis back on w/ a different code: P0420 Catalyst Efficiency Below ThresholdBank 1. Could this be due to the crack in the exhaust manifold or a bad cat. Also, I had this code several months ago, deleted it and it stayedoff tillnow but in the mean timethe P0135 code happened. Thanks in advance for any advice.

 

It's probably a combination of both.

Unfortunately, with that exhaust manifold/catalytic converter setup, you can't change just the catalytic converter. The only solution is to get a replacement manifold/converter and have it installed, so really, if it's a result of the crack, or the converter, it wouldn't matter, because you've got to replace both at once anyways if you wish to maintain a factory exhaust.