How to Test Fuel Injectors - Ensuring the Injectors Are Receiving Power

1. Turn the key to the “on” position without starting the engine. To conduct this test, the vehicle's electrical system must be active without the engine actually running. Insert the key and turn it until the electrical system activates, but stop before you engage the engine's starter. This should activate all of the vehicle’s electronics like interior lighting and the radio.

• If you accidentally start the vehicle, simply turn it off and try again.
• The vehicle’s battery is powering everything during this test, so you should turn off things like the headlights and stereo to conserve power and ensure it has enough to start the vehicle again later.

2. Connect a test light to the negative terminal on the battery. A test light looks like a screwdriver with a finely pointed end and a wire hanging out of the handle. When the wire from the handle and the pointed end come into contact with a completed and powered circuit, a lightbulb lights up inside the handle of the test light. The wire extending from the handle will have an alligator clip at the end. Attach that alligator clip to the negative terminal of the vehicle’s battery.

• You can identify the negative terminal on the battery by looking for the negative symbol (-) or the letters NEG.
• Make sure the clip has a good metal on metal connection to make the test light work.

3. Locate the two wires going into each injector. Each fuel injector will have a metal clip plugged into it with two wires coming out of it. One of those two wires is a 12-volt constant that should be continuously receiving power from your vehicle’s electrical system. There should be a small portion of each wire exposed coming out of the plastic clip that connects to the injector.

• These wires are often grey and black, but can come in any number of colors.
• They will be the only wires coming from each injector.

4. Test each wire for voltage. Take the sharp end of the test light and press it firmly into the rubber coating around each wire until it penetrates into the metal wiring itself. One of the two wires should make the test light turn on when it comes into contact with the wire inside the protective coating. If the test light turns on with one wire, then the injector is receiving the necessary constant voltage.

• Make sure to wrap a piece of electric tape around any holes in the wiring’s protective coating that are big enough to see.
• If neither wire makes the light turn on, then there is an issue with the power reaching the fuel injector, which will result in in failing to fire.
• If the all of the wires that light up are a certain color, make note of which wires are the constants.

5. Repeat the process for each injector. Test each wire coming out of the fuel injectors in your vehicle. If you locate one injector with a power issue, that doesn’t mean others may not have the same problem. Once you identify an injector with a power issue, make a note of which one it was and continue to test the rest.

• Follow the wires on the injectors that fail to engage the test light to make sure there are no breaks in the wire that may prevent the electricity from reaching it.
• Let your mechanic know that you were able to identify the injector with a power issue. It may require replacing the vehicle’s electronic control unit.