Methods and systems are provided for detecting NOx sensor degradation based on results from a NOx sensor self-diagnostic (SD) test. In one example, a method may comprise: determining that a nitrogen oxide (NOx) sensor is degraded if outputs received from the sensor via a CAN bus during a self-diagnostic test are outside a threshold range. Additionally, only outputs received from the sensor during a self-diagnostic (SD) test performed after a first completed SD test after a key-off event, where the outputs are generated under conditions where a temperature at the sensor is less than a threshold, and an oxygen concentration is within a threshold range may be used to determine if the sensor is degraded.