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Does the 04 civic lx have an afr sensor? The previous owner installed stainless steel headers that has a hole for the afr sensor. The plug from the harness is not where it’s supposed to be on the engine and I can’t find it so that’s why I was wondering if it had it.

 
Rep Power: 367

that's called o2 sensor
any modern car with fuel injection have them (back from the 1990's), heck, even carbureted cars can have them, although not for controlling injection since carbureted

 
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I understand that but from my understanding the car has three o2 sensors but the manifold sensor is the primary one to determine afr

 
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I’m just trying to make sure that I’m right I’m thinking there is three o2 sensors and how to trace the wiring harness to find the one for the manifold sensor

 
Rep Power: 367

only HX/Hybrids have 3 sensors
the one for the header is just behind the radiator

 
Rep Power: 367

maybe HX only have 2

 
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I’m missing the plug from that part of the harness but the wiring diagrams I was looking at show they run off of the same wires as the one just below the headers. I was rhi going about splicing the other plug and wiring in the sensor in the manifold to the the other o2 sensor

 
Rep Power: 367

2nd one is just to tell that cat is working. wiring them together is gonna cause issues