04 Civic HX replaced tranny...
 

Brief history: Bought this car in Feb as something to learn car stuffs on (This isn't my cup of tea, but no other way I figured I'd learn)

It was bought with a CEL P2646, which I still haven't replaced the Solenoid yet (just driving a short distance to work, so the 4k limiter wasn't really a bother, didn't really see it as an "Immediate issue")

ran it a while, unknown to me that the transmission had a leak and that fluid was ridiculously low, and in early April it seized.

Had it replaced, and within 100 miles that one started to leak as well.

Just got the car back last week and two things have happened:
I now also have CEL P0134 (o2 Sensor Circuit no activity) and P0420 (Catalyst System Efficiency Below Efficiency) [I get notified of new CELs on my phone thanks to my BT OBD device] - I tested the first o2 sensor and it is indeed bad


AND My car used to limp out / hit 4k rpm at: 60 in 3rd, 80 in 4th, and 100 in 5th. Since getting my car back it now limps at 47, 60, and 80.

Not sure if the power issue is due to the tranny or the o2 sensor issues I have.

Today I went down to a pick a part type of place and picked up an O2 sensor from a 99 civic, didn't know if it would work or not, but decided **** it, let's try. Threw it in and immediately got codes P0141 and P1130 where now I'm kinda stuck.

Re: 04 Civic HX replaced tranny...
 

You absolutely cannot do this, the sensor needs to be an AF sensor not an O2 sensor. they look feel and smell the same, but they are not compatible and not interchangeable.