Fuel Injector Test

Step by step guide on how to test an automotive engine fuel injector, this information pertains to electronic fuel injected vehicles, not direct injection.

A fuel injector has two main sections, the electrical portion which activates the valve assembly and allows fuel to enter the engine. This guide will check both aspects along with the trigger and power circuits supplied by the computer.

Difficulty Scale: 4 of 10

Begin with the vehicle on level ground with the engine off and the parking brake set. Fuel maybe present during these tests, usual fire precautions are necessary. Use protective gloves and eyewear for safety.

Step 1 - Start the engine and allow to idle, using a long metal rod like a screwdriver touch the end of the rod to the injector, gently lay an ear to the opposite end of the rod or handle to observe an audible clicking sound, repeat this procedure across all injectors, this can help pinpoint the failing injector. (Note: This sometimes can be difficult because of internal engine noise.)

Audible Fuel Injector

Step 2 - With the ignition key turned to the "ON" position without starting the engine, connect a test light to the negative side of the battery and probe the injector wires, one of the wires should illuminate the test light. If a volt meter is used the multimeter (voltmeter) should bounce from 0 to 12  volts. If system power has been disrupted suspect an injector or computer fuse, broken or shorted wire or bad computer, (Note: Seal test points with a small dab of silicone rubber once testing is complete) this test can also be performed with the connector removed as well. Some vehicle computer feed wires are located near the battery, corrosion can stop the voltage feed. If all power sources check out the computer system ground needs to be checked, this is done by reversing the test light lead by installing it on the positive side of the battery which will cause test light to illuminate when grounded, most system ground wires are black but to be sure an online auto repair manual is needed.  If repairs have recently been made a system ground lead could have been left off of the engine causing the system not to power up, double check all engine wiring harness grounds.

Test Light Probe Injector Wiring

Step 3 - While the test light clamp is on the positive side of the battery, move the test light probe to the opposite wire in the injector connector, have a helper start or crank the engine while observing the light, when cranking or under load the light will flash brightly, when idling or easy throttle the light will flash more dimly. This trigger circuit for the injector is supplied by the computer and follows the throttle and engine demand. If these test revealed that there was no pulse and the computer has power and not generating a fuel injector trigger signal suspect a crank angle sensor, (engine not running) or shorted computer or sensor. A shorted injector can hinder the injector driver operation for additional injectors, unplug all injectors and re-test pulse trigger, if pulse returns, plug the injectors back in one at a time until the pulse fails, replace the shorted injector. If tests check okay, proceed to next step.

Test Light Flash

Step 4 - A voltmeter is used in this test, adjust the meter to the ohms setting, these next steps can be performed with the injector installed or uninstalled.

Multi Volt Meter Set To Ohms

Step 5 - Identify the injector to be tested and inspect for defects or bad connections.

Fuel Injector


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2015-01-08)