I have a 2004 Ford Explorer and when you turn the key it won't do anything. I have had the battery, starter, fuses, ignition, and relays all checked and they're all good. I even tried jumping the starter off and it turned the motor over but would not crank. Had it hooked up to a diagnotis machine and it come but reading an error. It won't show any codes. What could it be?

Hello, What you are saying is the starter will turn if you jump the starter Relay. If you want to try this a second time, make sure the Ignition switch is in the RUN position. It should start.

Be sure to have the vehicle in Park. There are some Interlocks in the gearshift and Brake pedal that prevent when certain things happen. When your vehicle is in Park or Neutral, the power wire from the Ignition switch can make a connection to the wire that controls the starter Relay.

But first this wire has to get the okay from the Interlock switch, that the gearshift IS either in Park or Neutral. If this switch is bad or misaligned, the connection will not reach the starter Relay. You need to take off the small wire at the starter Relay and hook up a test light or meter. Then turn your Ignition key to START. The small wire should have power when the key is held in the start position.

If the small wire does not have power, then everything connected to that wire needs to be traced back to the Keyswitch. The cables or rods that move in the gearshift or steering column may be out of adjustment. Not too expensive to correct.

I hope my solution is very helpful to you.