Got a 2000 civic ex, and have codes PO135 and PO505. I know what the codes are. First one is Front O2 sensor, second one is Idle air control. I assume the O2 front sensor is the first one coming off the pipe at manifold?? What would idle control code be from? Defective valve? Do you think replacing the O2 alone will pass e-test...tight for money right now, looking for a fix. it was way over on the E-test like 2136 or something...dont remember?
I dont want to change the O2, then find out the cat or something is screwed. Anyone have any Idea of the likely problem based on your own experience? Or do these cars have a common problem, like maybe the cat that sends out the PO135 code? Or would that 505 code be the culprit or both. Just need a start somewhere....Thx alot

 

The general rule when there is more than one code is to reset the codes and see which one reoccurs first.

But since you already know it fails the tailpipe sniffer, it's a good bet that O2 sensor is bad. It is the one closest to the engine, before the converter. Generally if there's a problem with the cat you will get the code for the other sensor. The second sensor is just to check the performance of the cat.

The idle control code is probably nothing. It will be set whenever the idle speed is out of control for whatever reason. Problem is you will fail the e-test if the CEL is on for any reason. If it reoccurs try cleaning the IACV.

So in a nutshell replace first O2 sensor, reset all codes, drive at least half an hour, see if CEL stays off. If so take for re-test.

 

P0135:
First check whether fuse 15 under the dash is blown.

P0505:
This code is more complicated. Is the idle speed too high or too low? The possibilities are bad IACV, TPS, or ECT sensors, as well as a vacuum/intake air leak or the idle needs to be adjusted.

 

Ok, Im gonna check that #15 fuse, if its ok I will replace the O2sensor and clear the codes. With the 505 the IAC valve. Where is that located? I had problems with these IACs before on a mercury mystique I had...I find they gum up and stick so that might be worth cleaning anyway before I clear the codes. Its my daughters car....so I never really drove it. She just told me it failed the E-test...so I hooked my scanner on it and pulled the 135, and 505 codes. Any advice on the O2 sensor...Some are like almost $200 and I can get a universal one cheaper for $134. Does it matter what brand, or is the aftermarket ones ok as well?

 

Is there an idle problem? Too high, too low, hunting?