Symptom and cause of a malfunction are sometimes worlds away from each other! This is shown by the following case: a Ford S-MAX with the engine code QXWA and model year 2010 came into the workshop. The problem: at irregular intervals, it could not be turned off even after removal of the ignition key. The engine continued to run and had to be stalled while the gear was still engaged. A short stay in the workshop did not produce a useful result either. No errors whatsoever were stored in the error memory of the control units.
The workshop staff checked all known sources of error in the starting system and ruled them out. But then, by chance, when the hatchback was opened to a certain position, the engine stopped. The mechanics successfully simulated the scenario once again. After a closer inspection, they came across something unusual: in the kink of the wiring harness of the hatchback, they found some individual cables that had been damaged. Because these were in contact with one another, voltage transitions and reverse currents to the fuse box resulted. This in turn resulted in terminal 15 (ignition plus) not being switched off safely, although the ignition key had been removed.
Check wiring harness and replace if necessary. One more note: as the wiring harness is subjected to increased loads in this area, partial repair may only be of a short duration. For this reason we recommend the complete replacement of the hatchback wiring harness.