How to Test Injector Wiring

by Skip Shelton

Fuel injectors operate though the brief charging of a solenoid and subsequent opening of a valve. The opened valve allows pressurized fuel to be pushed through the fuel injector nozzle into a fine spray. The solenoid is engaged when a 12-volt current is provided by the electronic fuel injection system. The electrical connection to the fuel injector may be hampered by shorts in the wiring, inadequate voltage at the injector plug, or incorrect resistance in the fuel injector.

Electrical Short Testing

Disconnect all the fuel injector electronic plugs on the engine.

Set a multimeter to "volts." Connect the multimeter's red lead to one of the disconnected plugs. Connect the black multimeter lead to the vehicle battery's positive terminal.

Have an assistant start the engine. The engine rotation will charge the fuel injector electronics plug. As the engine turns, the voltage on the multimeter should alternate between 12 volts and 0 volts. Keep the multimeter attached to the plug.

Connect one of the other fuel injector plugs to the associated fuel injector. Turn over the engine and recheck the voltage on multimeter. Continue attaching more plugs and retesting until all plugs are attached or until the multimeter fails to display a 12 volt to 0 volt alternation.

Replace the injector associated with the plug which, when connected, resulted in the multimeter test failure. A shorted fuel injector will prevent electricity from activating the solenoid in the other plugs.

Voltage Testing

Turn the ignition key to the "On" position. You do not need to start the engine for this test.

Disconnect the electronics plug wire from the fuel injector.

Turn the multimeter to "volts." Insert the black and red multimeter leads onto each side of the fuel injector electronics plug. Because you are testing the current it is not necessary to have a specific lead on a specific side of the plug.

Read the multimeter. The voltage should read approximately 12 volts.

Replace the wiring for any single wire set which fails the 12-volt test. Be sure to test all the wires before replacing any single set. Mass failures may indicate a failure in the electronic fuel injection relay or the engine control module.

Fuel Injector Resistance Testing

Turn the multimeter to "Ohms."

Place the multimeter leads into the fuel injector plug terminal. It is not necessary to have the black or red leads on a specific side of the plug terminal.

Read the Ohms, or resistance, produced by the fuel injector. Note the value or write it down.

Test all the fuel injector Ohm readings. Compare the value of each reading to the other values. Operational fuel injectors will have the same, or very similar, Ohm values. A failed injector will have too little or too much resistance and the Ohm value will be widely different than the other readings.

Replace the injector if the Ohm value is significantly different than other injectors. Failed injectors may still fire, leading you to believe the problem is in the wiring.


  • Inspect the fuel injectors for leaks before performing electrical tests. Leaking injectors may cause fire hazards.

About the Author

Skip Shelton has been writing since 2001, having authored and co-authored numerous articles for "Disclose Journal." He holds a Bachelor in Science in education and a Master of Business Administration with an emphasis in management from Northwest Nazarene University. Shelton also operates a small automotive maintenance and part-replacement shop.

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