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Long story short my 05 Honda was totaled. The motor (D17A1 non vtec) was still new as it was freshly redone so I saved it and installed it into a doner car 03 Honda civic EX that had a D17A2 (vtec). I swapped my good engine, harness and ecu. Everything runs great and I have no issues other than this darn PO135 code. I have replaced the 02 sensor with a brand new factory one and still get the code. It pops up within 5 seconds of resetting. Any input would help me out! Thanks

 
Rep Power: 368

which sensor did you get?
for the 03 or 05? Which exhaust are you using?
Did you get Denso or NTK sdensor?

 
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since everything is now, 05 I bought the new sensor for an 05. It was factory Honda, which is made by Denso. I also tried my original one from my 05 which I never had any issues on. As far as the exhaust, I am running the 05 manifold and I had to modify the current 03 exhaust to lineup correctly to the 05 manifold as it was a different downpipe. The original cat that the car came with is still within the exhaust system, but it’s towards the center of the car. I left it there and plugged the sensor thread because I didn’t think it would have any effect on the current set up.

 
Rep Power: 368

?!? so you are running two cats?!?

 
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Yes technically. But the second one is in the middle of the exhaust system and I have the two sensors on the original manifold that has the built in cat as it came with the motor that in it. There is no sensor to the rear existing cat. I can cut it out but I didn’t think it would make a difference or hurt anything because it’s after the two sensors I’m using now.

 
Rep Power: 368

loosen exhaust between both systems and see what happens

 
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Unplug the sensor, turn car to II and measure the voltage of the two heater wire pin on the plug, is it 12v?

 
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no change