A lovely condition BMW Z4 came into the workshop yesterday that had an intermittent ‘non-start’ fault. The vehicle would sometimes just not start or turn over. Nothing. Dead. The battery was good and the ignition dash lights would illuminate. We carried out two very simple tests. One: testing for power between the EWS module and starter solenoid. In a non-start situation, there was no power between these two. We had to test further back. Was the EWS module receiving power and not functioning as it should or was the EWS module not receiving any power at all? The second test we ran was testing for power between the ignition switch and EWS module (attached image). In the non-start situation, the ignition switch was sending no power.
Running these 2 tests allowed us to pinpoint where the fault lay. On this occasion, the starter motor was fine, the EWS module was fine and therefore the ignition switch was at fault. Upon replacement of the ignition switch, the vehicle started first time, every time.