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I am having lots of trouble resolving a P0135 code on my 2004 Honda Civic DX. There is one sensor before the catalytic converter and a second sensor immediately after. P0135 I believe refers to the O2 sensor that lies before the catalytic converter, so I replaced it, but I'm still getting the error code after resetting the ECU. I've tried several O2 sensors and keep getting the error code.

I replaced the downstream O2 sensor as well, still getting the same code.

Are both the upstream and downstream sensors O2 sensors? Some people said the upstream is an AF sensor, but I think that's the same as an O2?

Also, if the O2 sensor is good, what voltage/resistance values should I be seeing on the wiring harness in case it's an ECU problem?

Thanks!

 
Rep Power: 119

It’s a AF sensor, not the basic O2 sensor.

Some have gotten the $100ish denso direct unit to work, always the $250ish oem one works, frequently people buying generic end up on the forum because it still isn’t working..

always possible is not the sensor but a wireharness / ECU issue.

 
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Thanks for the info.

If it is damage to the wiring harness/ECU, do you know what voltages/ohms I should expect between the pins? I can't seem to find that info.