Methods and systems are disclosed for imminent read failure detection based upon changes in error voltage windows for non-volatile memory (NVM) cells. In certain embodiments, data stored within an array of NVM cells is checked at a first time using a diagnostic mode and high/low read voltage sweeps to determine a first error voltage window where high/low uncorrectable errors are detected. Stored data is then checked at a second time using the diagnostic mode and high/low read voltage sweeps to determine a second error voltage window where high/low uncorrectable errors are detected. The difference between the error voltage windows are then compared against a voltage difference threshold value to determine whether or not to indicate an imminent read failure condition. An address sequencer, error correction code (ECC) logic, and a bias generator can be used to implement the imminent failure detection.