Without using scan tool MB991502

Turn the ignition switch to the "ON" position while holding the auto-cruise control switch in the "SET" (down) position. Then, within one second, move the auto-cruise control switch up to the "RES" position.
Check to make sure the "CRUISE" light on the instrument panel is flashing.
Put the auto-cruise control switch in the "SET" (down) position. Depress the brake pedal and hold for five seconds or more. Release the brake pedal, auto- cruise control switch, then turn the ignition switch to the "LOCK" (OFF) position. The DTC(s) are now erased.

Fig 1: Erasing Diagnostic Trouble Code Without Using Scan Tool MB991502
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.