Lambda codes caused by blown exhaust?

[TomStreet]

I’ve got an 05 Ford Fiesta ST150 MK6, have had the engine light on for a little while with the fault codes P0141 and P0138. I’ve come to the conclusion it’s likely the after cat lambda sensor and have prepped a new one to swap out. Tonight however it’s become really clear that the exhaust is blowing. Could it be possible that these fault codes could be put down to this, or is it two separate issues? Would really appreciate any advice.

[Jazoli]

If the exhaust is blowing upstream of the lambda its not unusual to get an EML and fault codes for incorrect readings.

[TomStreet]

Appreciate the reply, thank you