I own a 2018 Fiesta ST-Line and the check engine light came on a few days ago.

I bought an OBD reader out of curiosity, and it’s coming up with the code P0036 - H02S Heater Control Circuit Bank 1 Sensor 2.

As I am a complete newbie when it comes to stuff like this, I have been looking online to try and work out how to fix it. As far as I’m aware, it’s one of the sensors that fits the catalytic converter. I’m also getting conflicting information on where it is. I’m not sure if it’s under the car, or near the engine.

Can anyone please advise me on how easy it is to fix, or whether I should just take it to a garage?

Also, is it safe to drive? Or should I avoid high mileage until it’s fixed?

Thank you!

Sensor 2 is the one after the cat.  So that is under the car but still near the engine.

(Sensor 1 is right on top at the front, sticking out through the shiny turbo heat shield, just for reference)

I'm theory it's easy to swap the sensors.  Just unplug & unscrew one, then screw in and plug in the new one.  Though it can be difficult if access is tight or it's seized in with heat cycles.

Also worth noting this fault isn't always fixed with a new sensor on this engine, though I'm sure you've seen that through Googling.

Yes it's safe to drive in the meantime.  I wouldn't change driving style at all for this code.

4 hours ago, TomsFocus said:

Sensor 2 is the one after the cat.  So that is under the car but still near the engine.

(Sensor 1 is right on top at the front, sticking out through the shiny turbo heat shield, just for reference)

I'm theory it's easy to swap the sensors.  Just unplug & unscrew one, then screw in and plug in the new one.  Though it can be difficult if access is tight or it's seized in with heat cycles.

Also worth noting this fault isn't always fixed with a new sensor on this engine, though I'm sure you've seen that through Googling.

Yes it's safe to drive in the meantime.  I wouldn't change driving style at all for this code.

Thanks Tom, much appreciated! Just what I was looking for.

Unclip the electrical connection first otherwise you will twist all the cable up, when refitting, screw the sensor in first and then plug it in to the harness to avoid the same problem.