Fluid injector

1. A fluid injector for a selective catalytic reduction dosing system comprising:

a coil arranged to drive a pump from a first state to a second state when energized, so as to pump and inject a fluid;

a PN junction electrically arranged across the coil to breakdown and discharge energy stored in the coil when an external drive voltage is removed from the coil, and when a voltage across the coil is above a breakdown voltage of the PN junction, and wherein the PN junction and the coil share a cooling system.

2. The fluid injector of claim 1 wherein the PN junction is within a diode electrically arranged across the coil.

3. The fluid injector of claim 1 wherein the PN junction is within a transient voltage suppressor electrically arranged across the coil.

4. The fluid injector of claim 1 wherein the PN junction is directly connected to the coil.

5. The fluid injector of claim 4 wherein the PN junction is soldered to terminals of the coil.

6. The fluid injector of claim 1 wherein the PN junction and the coil are within a common cooling jacket.

7. The fluid injector of claim 1 wherein the selective catalytic reduction dosing system comprises a diagnostic circuit configured to diagnose the satisfactory operation of the PN junction, wherein the diagnostic circuit is arranged to measure a current decay or a voltage delay during discharge of the coil.

8. The fluid injector of claim 1 wherein the fluid injector is one of a selective catalytic reduction dosing injector, a fuel injector and a water injector.

9. A method of discharging a coil of a fluid injector, the method comprising:

supplying a coil of the fluid injector with electrical energy to drive a pump from a first state to a second state so as to pump and inject a fluid;

stopping the supply of electrical energy to the coil; and

allowing the electrical energy stored in the coil to dissipate through a PN junction electrically arranged across the coil and wherein the PN junction and the coil share a cooling system.