How To Diagnose A Failing Fuel Injector

If your Toyota car or truck is sputtering or running rough, it can be difficult to diagnose the issue. Fortunately, modern cars use onboard diagnostic codes, or OBD-II codes, to highlight issues with your vehicle's engine, including problems with the fuel system. If the problem is fuel related, it's usually a problem with the fuel flow. And if the vehicle still runs, the most common issues involve the fuel filter or a fuel injector.

In this guide, we'll cover the fuel injector and how to diagnose one that's failing.

What Is A Fuel Injector?

Fuel injector

A fuel injector is a device that delivers a high-pressure spray of fuel into the engine's combustion chambers. Most modern cars have one injector per cylinder, so if you have a six-cylinder engine, you more than likely have six fuel injectors. Each injector uses an electronic signal to tell it when to spray the fuel and how much to provide. Learn more about what injectors do in this post.

What Are Some Signs Of A Failing Injector?

As a fuel injector wears out or gets clogged, it starts to spray either too much or too little fuel in the combustion chamber. That problem leads to one or more of the following symptoms when you drive your vehicle:

  • Engine misfires or runs rough
  • Rough or uneven idle
  • The tachometer begins to twitch or shake
  • Poor fuel economy
  • The vehicle is hard to start, including excessive cranking or requiring multiple attempts.

Troubleshooting A Failing Fuel Injector

Clogged fuel injector

When a fuel injector fails, it's either due to an electrical or mechanical issue. This is where a good OBD-II scanner comes in handy.

Electrical-related fuel injector problems trigger a P0200 to P0208 code. A P0200 code indicates a general fault or problems with multiple injectors. P0201 to P0208 codes indicate a problem with a specific injector - for example, P204 would indicate the problem is with the fuel injector for the #4 cylinder.

Fuel-related OBD-II codes are in the P0300 to P0308 range. The format is the same as the electrical codes, with P0300 indicating a general issue or multiple injector problems and P0301 to P0308 indicating a problem with a specific injector.

To confirm the codes and verify you have an actual issue as opposed to a one-off misfire, you have two options:

  1. Clear the codes using your OBD-II scanner and drive your vehicle. If the error codes reappear, it means you have an issue with one or more of the fuel injectors.
  2. Start your vehicle with the OBD-II scanner plugged in and look at the real-time codes, which show problems that are occurring. If the error codes appear while the engine is running, that indicates a problem with one or more fuel injectors.

Other Items To Check

Before you replace one or more fuel injectors, there are a few other things to check or consider:

  1. If you get a general P0300 or multiple P0300 series codes indicating misfires on multiple cylinders, it could mean you have a partially clogged fuel filter. A partially clogged fuel filter will starve the engine of fuel and create the same symptoms as a failing injector.
  2. If the error code identifies a specific cylinder, check the spark plug for that cylinder alone to make sure it's not dirty or fouled.
  3. fuel pump issue can also cause similar symptoms but will show up as a P1228 code on your OBD-II scanner. 

Shop For High-Quality Fuel Injectors

OEM toyota fuel injectors

After all the work you put in to diagnose your fuel injector issue, do yourself a favor and replace the part with an OEM part from Olathe Toyota Parts Center. We only sell genuine OEM fuel injectors and other Toyota parts at wholesale prices.

We also offer helpful resources like diagnostic info for common Toyota trouble codes, a free Toyota VIN decoder, and a wide variety of other resources just for Toyota and Scion owners. If you've got questions about the fuel injectors in your car, or need assistance in finding the right OEM parts, just give us a call!