Code 12 (No RPM Signal)
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1990 Toyota Pickup, 1990 Toyota Cab & Chassis, 1990 Toyota 4Runner, 1989 Toyota Pickup, and 1989 Toyota Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
ECU will store trouble code No. 12 in memory if it does not receive signal from either "NE" pick-up coil (RPM) or "G" pick-up coil (crank position) within 2 seconds of engine cranking.