Hola Hector,
Senor Joe is correct.
A steer card usually fails from overheating because the drive unit radial rings are worn and cause the steer motor to over amp from drag. jack up truck and measure drive unit play with a dial gauge. There should be no more than 100 thou play! Also look under at the drive unit and check for contact of the drive unit ring and drive unit. If worn, there will be contact causing grooves. the drag will overheat the steer motor and blow the steer card!!! you may require mucho pesos to fix this! When the radial rings wear, there is tremendous drag on the steering, but the driver wont feel anything...just the steer motor feels the excess force.
G4 is the vehicle mgr did not detect neutral pulses. Usually this is going to be a steer amp failure.