The present invention relates to exhaust diagnostic systems and methods with SCR conversion efficiency monitor disabling. A diagnostic control module includes a temperature gradient module. The temperature gradient module determines a temperature gradient across a selective catalytic reduction (SCR) catalyst of an exhaust system of an engine based on a plurality of temperature signals. A calibration module determines a weighted average based on the plurality of temperature signals. A SCR efficiency control module disables conversion efficiency monitoring based on the temperature gradient and the weighted average.