For 2 speed vehicles that will only operate on high speed:
Lift the drive wheels off the ground and check if both drive wheels turn when the gas pedal is pushed. If only 1 wheel turns, check to make sure that there are two wires connected to the motor on the opposite wheel. When re-plugging the wires on to the motor be sure that both wheels are turning in the same direction. If they are not, reverse the wires on one of the motors.
NOTE: A 1 speed vehicle is only supposed to have 1 wheel drive.

If the vehicle will ONLY operate in reverse or ONLY operate in low gear:
You may require a new switch. Contact your nearest Peg Perego service center.

If the stroller is difficult to steer:
Make sure the wheels closest to you (the back wheels) are locked to prevent them from swiveling and that the wheels furthest from you (the front wheels) are unlocked. Similar to a car, the front wheels do the steering while the back wheels remain straight. If the handlebar is reversible make sure to lock and unlock the appropriate wheels each time you reverse the handle. Do not unlock all 4 sets of wheels at the same time.

For easier steering on rough or uneven surfaces, try locking all the wheels to prevent them from swiveling.

If the stroller is pulling to one side:
Lubricate the wheel housing and suspension. If one side is spinning more freely than the other it will cause the stroller to pull to the side when pushing even on flat surfaces. If this doesn't solve the problem the vertical axel may be bent. This can be caused by hitting a curb or closing the trunk on the wheel housing. Contact your nearest Peg Perego service center.

Remember: Never force anything! If it has to be forced something is wrong, stop immediately and look for any obstructions.  If the problem isn't visible contact an authorized repair center. Continuing to apply force may cause severe damage.