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[Tripme]

Alright, a couple questions for you car guys.  As stated, I have a 2000 honda civic 4 door.  I recently had my check engine light come on so I drove over to autozone to have them check the error.  Turns out that the oxygen sensor is giving the error.  I got back and popped the hood and noticed I have two oxygen sensors.  One is before the cat, one after.

1)  What would be the best way to tell which one is bad?  (Assuming that one is even bad)

2) Should I check for anything else that could be causing the problem?

The parts I looked up online say that they either fit before or after the cat, so I wasn't sure what I should do now.  I don't want to straight up buy two replacements if I don't have too because, frankly, I can't afford it at the moment.  I could buy one now if there is a way to see which is bad (or if one will fit both locations)


Thanks for any advice.  If you need additional info, let me know.

[lordvader129]

did they tell you what the actual DTC was? it should indicate if its the upstream or downstream sensor

[rms2001]

They should have told you what one is causing the error. Did they clear the code for you? For a brief time I had a 2004 Toyota Tundra (you can thank this truck for me hating imports) that would through a code every few weeks. Mostly when I would drive to Phoenix and back with a trailer. I think the altitude change was so drastic in such a short time the computer couldn’t compensate quick enough and would tell me one of the 02 sensors is bad.  

I happen to own an OBDII scanner and was able to check and clear the code on the spot. It wouldn’t come back until I towed a trailer down there back. One day while replacing the fuel filter I took both of the 02 sensors out and cleaned them with brake fluid. Let them dry and reinstalled them. Never had that problem again with the truck. Wish I could say that about the rest of the problems it had…

Simply cleaning them mite do the trick. I know those little bastards are expensive. If you end up buying a replacement, make sure its has the OEM plug on it. Some times they will sell you a cheaper sensor with out the plug, that you will have to wire in wire by wire. This is another reason I went with a diesel truck, no emissions what so ever on it. Straight pipe from the turbo.

[Tripme]

I could take them out and clean them.  What would you say to clean them with?

I plan on taking my car back to another place to have the error scanned to see if they can tell me which sensor specifically is causing the problem.

Thanks

[twistedsymphony]

I've heard that autozone will do OBDII scans for free... they have better hours than most mechanics too  

[lordvader129]

QUOTE(Tripme @ May 15 2008, 12:55 PM)

I could take them out and clean them.  What would you say to clean them with?

I plan on taking my car back to another place to have the error scanned to see if they can tell me which sensor specifically is causing the problem.

Thanks

have them tell you the code too, should be P then a 4 digit number (probably P11xx) then you can look up what it means here

[hamwbone]

autozone is terrible with diagnostics of the actual DTC codes. nab the code from them and look online.  have them reset it, drive a few miles to fill up the memory bank, usually like 5 miles and 30, 5 miles at 60, then 5 miles and 40.  if it hasnt come back on try to get the inpection done or have them see if you OBDII system is in READY mode. then get the inspection.

[Tripme]

Went back to autozone for the scan.  This time was a lot more informative.  The guy gave me a printout of the code and what it meant.  It is the first oxygen sensor before the cat.  Error code was P0135.  He went ahead and reset the code since it was the only error.

Thanks for the help everyone....guess i just have to wait and see if the light comes back on

[StrictPuppet]

P0135 is for the heater circuit in the O2 sensor, Bank 1 Sensor 1 (up front).  This will not cause you any drive-ability issues, but it will return eventually.  Its almost always the sensor itself that is at fault but can also be the wiring or the pcm.
The pcm determines if the heater is working by measuring the current that flows through the heater circuit while it is commanded on.  You can check its resistance to get an idea if its totally screwed or not, if you disconnect the connector with the O2 sensor cold and measure with an ohmmeter between the 2 black wires(may be white, but there are 2 like colored wires in the 4 wire connector)  You should see 10-15 ohms resistance.  If it is out of spec with this, you will need to replace it.  I don't recommend after market o2 sensors, especially for Honda heater codes, they are very picky.  If you cant afford an OEM sensor you can use an NGK/NTK or Denso sensor as they are the manufacturer of the OE part.  They are not too hard to change, but depending on accessibility you may need an O2 socket.  The hex nut is 22mm(7/8").