Abstract: An engine control system for a vehicle engine includes an engine control module (ECM) that enters a modified sleep mode when the vehicle key switch is turned to the "off" position. In the modified sleep mode, all non-essential operating tasks normally executed by the ECM are disabled to place the ECM in a mode of reduced power consumption. In addition, various communications interrupts are disabled, except for interrupts associated with at least one external data transmission device. During the modified sleep mode, priority for communications with the external device are highest to permit external communication to and from the ECM using the external device. In this modified sleep mode, the vehicle operator or engine technician can download or upload data to and from the ECM memory. The ECM includes a sleep mode task module that is maintained during the modified sleep mode. The sleep mode task module controls a sleep mode termination timer (SMT timer) that counts the time the ECM is in the modified sleep mode.