Fuel Injector

03-04 wiring sample

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Fuel injectors are electric solenoids. They are spring loaded closed and opened electrically. They are supplied voltage from the Ignition relay and are grounded by the ECM. There are only 2 fuel injector drivers for the MPI engines. Four injectorsare fired by each driver. All four on each driver are fired at the same time. The amount of time (in milliseconds) that the injector is grounded is the amount of time the injector is open.This is the injector’s pulsewidth.

Injector Driver A Circuit

The diagram above shows the injector driver “A”circuit. The injector driver circuit is a “Low Side”driver meaning that the ECM controls the “Low”or ground side of the circuit. Each injector driver fires 4 injectors, 2 from each side of the engine. The injector driver B circuit drives the other 4 injectors.

There is only 1 fault code for each of the injector driver circuits, injector driver circuit A or B “High, Low or Open”. This fault code is set by what the ECM “sees”on the driver circuit back at the ECM. There are 4 parallel circuits through the injectors in 1 driver circuit. For the fault code to set, the open has to be (in the diagram above) above thesplice in the feed circuit or below the splice in the ground or driver circuit back to the ECM. If any injector has an open circuit in it, the code will NOT set. This is because there are still 3 more circuits (the other 3 injectors in that driver) carrying current. On the other hand, if the circuit is shorted to ground anywhere in the circuit, the fault will set. If the short is on the feed side, then the circuit protection device (fuse) will blow. If the short is in the ground or driver circuit, then the injectors will remain open with the key on until the injector coils melt and go open circuit (or short together and then blow the fuse).

Remember basic electricity; opens in parallel circuits only affect the leg that has the open. Short circuits affect the entire circuit.