land problem

On the diagnostic connector, pin 4 is ground and pin 5 is ground signal. I have a problem with the ground on pin 5, and the car won't start. It's a 2001 Fiesta. If I connect a ground wire directly, the car starts, but I don't know if that's the correct way. I think the ECU itself should provide that ground, but it's not doing so for some other reason.

Hi Anthony, your problem is strange. Locate a screw where the ECU grounds connect. From the driver's seat, on the left, touch the floor and the edge where the carpet ends. The screw is hidden underneath it. You might need to remove the small plastic floor piece nearby to lift the carpet. Check if the screw is loose, corroded, or rusted. Let us know how it goes.