I have a 2003 EX which was giving me a P0135 fault and pending, so I cleared the codes, but they came back within a few seconds. I replaced the oxygen sensor with the NTK OEM part but the two codes come back the same. So I followed the voltage tests at Part 1 -How to Test Trouble Code P0135 (2001-2003 Honda 1.7L) and got 12 Volts from both black/yellow and black/white for hot and ground, so I don't understand why this code would keep coming up. There is something I couldn't find any reference to online and I can't find any pictures of the wiring harness with view of the connection to the O2 sensor to figure it out: one of the wires is white which is supposed to be the sensor ground according to that troubleshooter: but a few inches up from the connector that white wire has a black wire... wrapped around it? What I'm trying to describe is that before it reaches the connector it is a black wire, but then it's stripped with a wire weave exposed, leaving only the white wire to go to the connector. But the connector back doesn't have spare room wide enough for that woven wire under the black to have fit... inside it? That's confusing: is this outer wire weave supposed to be half of a ground/positive loop as a single wire, and somehow it got broken and stripped? Since this is the only thing about the situation I don't understand I'm figuring that it's the problem. Any expertise would be greatly appreciated.
-B

 

maybe you have a bad cat? and maybe that wire is a patch wire someone used because they stripped the original black one when diagnosing it for something...

 

P0135 indicates that the upstream oxygen sensor isn't warming up fast enough, which shouldn't be at all affected by the cat.

 

Did you test the sensor? DId you pull it from a junkyard?

Test the connectors with a multimeter, test the sensor, you might have a break in a wire...who knows...

 

I'm confused by your response: I did test the harness wires for the heater like I said. I will test the sensor itself when it's cold for accuracy on resistance, but I doubt that this brand new (from a parts store) oem part is defective. I was also very careful not to remove the protective cover until installation, and the sensor end never touched anything during install. Who knows is why I'm here: to find them.

 

My guess is you are currently replacing the downstream sensor instead of the upstream one.