Methods and systems for estimating exhaust pressure with a variable voltage oxygen sensor

A method, comprising:

• during engine fueling conditions:
• generating a first output of an oxygen sensor operating at a target reference voltage where water molecules are dissociated when an air-fuel ratio is at a first level, the oxygen sensor disposed in an engine exhaust passage;
• subsequently generating a second output of the oxygen sensor operating at the target reference voltage when the air-fuel ratio is at the first level;
• and
• estimating an exhaust pressure of exhaust gas flowing though the engine exhaust passage based on a difference between the first output and the second output.

A system for an engine, comprising:

• an exhaust oxygen sensor disposed in an exhaust passage of the engine upstream of a catalyst;
• and
• a controller with computer readable instructions for:
• adjusting engine operation based on an exhaust pressure of exhaust gas flowing through the exhaust passage, where the exhaust pressure is estimated based on a first output of the exhaust oxygen sensor while operating the exhaust oxygen sensor in a variable voltage mode where a reference voltage of the sensor is at a target voltage where water molecules are dissociated and while operating the engine at a first air-fuel ratio and a second output of the exhaust oxygen sensor obtained a duration after the first output, while operating the exhaust oxygen sensor at the target voltage and while operating the engine at the first air-fuel ratio.