Forgetting the flyback connection can cause serious damage.

18V unidir transient diode

* eg. SMBJ18A (or SMAJ18A 18-21.1V Ubr 400-600W UNIDIR.)

* SMD diode cathode=EC36/23 flyback and anode=EC36/22 ground on the underside of the v3.x is useful (not essential, but been present on most assembled ECU-s since appr 2013).

* Might provide some last chance protection in case of seriously bad install (flyback forgotten).

* If flyback connection is good, the circuit functions without that diode.

** If the diode is burnt: (only possible with serious wiring problem: after fixing the harness: adding flyback connection to the injector shared +12V)

** preferrably replace SMBJ18

** or use a beefier throughole unidir transient diode: 1.5KE18A 18V (1500W UNIDIR DO-201), inside ECU or in the harness (no problem if there is a diode already)

** or just remove if no spare (damage will be more serious if wiring is not fixed, or flyback connection breaks/disconnects later).

----