Systems and methods for detecting exhaust air leak

A method, comprising:

• oscillating an air-fuel ratio of an engine;
• indicating an air leak in an exhaust passage of the engine based on a measured pressure at a particulate filter coupled downstream of an exhaust catalyst;
• adjusting a threshold for a monitor routine of an oxygen sensor responsive to the indication of the air leak, the oxygen sensor coupled downstream of the catalyst;
• and
• indicating a degraded sensor response based on oxygen sensor output during the air-fuel ratio oscillation relative to the threshold.

An engine system, comprising:

• an engine;
• an exhaust passage including an exhaust catalyst;
• an upstream oxygen sensor coupled upstream of the exhaust catalyst;
• a downstream oxygen sensor coupled downstream of the exhaust catalyst;
• a particulate filter coupled downstream of the downstream oxygen sensor;
• a pressure sensor coupled to the particulate filter;
• and
• a controller with computer readable instructions stored on non-transitory memory for:
• responsive to entry conditions for a first monitor routine of the downstream oxygen sensor being met,
• comparing an output of the pressure sensor to a threshold pressure;
• and
• raising a threshold of the first monitor routine responsive to the output of the pressure sensor being higher than the threshold pressure;
• executing the first monitor routine;
• and
• indicating degradation of the downstream oxygen sensor responsive to an output of the downstream oxygen sensor exceeding the raised threshold following the executing of the first monitor routine.