maintenance > Rear Oxygen Sensor

Why did you swap out the rear oxygen sensor on your RS?

All sensors will eventually quit responding and cause a Check Engine Light (CEL) on most newer automobiles. The rear oxygen sensor, in particular, measures the effectiveness of the catalytic converter. In my case, the heater circuit of the rear oxygen sensor malfunctioned and caused a CEL code of P0054 "HO2S Heater Resistance Bank 1 Sensor 2".

No clue why the sensor failed on my 2016 RS with just 6,259 miles. It could be the extra power I'm making (including E30 fuel), the vibration from basically solid motor mounts and lack of balance shafts, or just a cheap OE sensor.

After swapping out the rear oxygen sensor, I reset the codes through my Cobb AccessPort.

Date Completed:



- Rear Oxygen Sensor (#FB5Z-9G444-A or alternate)
- Sweet Tea (optional)


- 1/4" drive ratchet, 6 inch extension (T-25)
- Flatblade screwdriver
- 7/8" combination wrench
*A friend for moral support is always optional. If friend isn't available Pandora will suffice.


1. Install takes about 30 mins or so. I took my time because of taking pictures for this website.
2. A total of (2) wiring plugs need to be disconnected for this swap (both front/rear oxygen sensors for access).
3. The bottom tray will need to be taken off for access below the engine.
4. I have a J-style restrictor already for the rear oxygen sensor, and it faces forward.
5. Follow along in the pictures for removal/replacement process.
6. Leftover parts = OE Focus RS rear oxygen sensor (broken).
7. Mileage at repair = 6,259.