I went for a drive today with the new O2 sensor installed from last night, and right around when the car gets to about 80c on the temp gauge, the check engine light comes back on. I pull over and check the codes on pin 3 and get the same 17 annoying blinks. Code 17 - oxygen sensor is shorted to positive or ground.

I remembered that I had a spare ECU that is allegedly good so I decided tonight to swap out ECUs. I also found a brand new OVP relay in the same box and put that in for good measure.

After the ECU swap I go for a drive and the check engine light comes on yet again. So again I pull over, check the codes, but this time pin 3 blinks once. No codes! I drive around the neighborhood for another 15-20 minutes and when home I check for codes in pin 3 and AGAIN I get code 17.

I've got a new O2 sensor and a "new" ECU and I'm still getting code 17 after repeatedly clearing codes. Looks like it's time to chase down this short.

I'm going to start tomorrow by directly grounding the o2 sensor temporarily with some wire to check for a weak ground through the exhaust. I know that's unlikely but I'd like to exhaust all my options before turning my attention to the wiring. I wasn't getting codes prior to dismantling the exhaust so there's a chance that something in that process is the root cause.

Any input would be greatly appreciated, as always.