How To Do A Fuel Injector Noid Light Test (GM 3.8L)

A fuel injector, on your 3.8L V6 GM vehicle (Buick, Chevrolet, Oldsmobile, Pontiac) can stop working and cause a Rough Idle and/or Misfire Condition if it doesn't get power (12 Volts) or its injector pulse signal from the PCM. Of course, this will light up the check engine light on your instrument cluster and if you're specific vehicle is OBD II equipped, you'll get Misfire Codes (P0301, P0302, P0303, P0304, P0305, P0306) stored in the car or mini-van's computer.

This article will show you how to perform a fuel injector Noid light test to find out if the fuel injector in question is getting both of its signals. This article supplements the information in the article: How To Diagnose Misfire Codes GM 3.8L 6 Cylinder (P0300-P0306).

Tools You'll Need:

  1. Fuel Injector Noid Light.
  2. Multimeter
  3. A Helper

The Fuel Injector Noid Light Test

Before attempting the fuel injector Noid light test on your 3.8L equipped GM car or mini-van, please read this entire article first and familiarize yourself with the testing information provided. This is a very fast and easy test:

  1. 1

    Disconnect the fuel injector you're going to test from it's electrical connector.

  2. 2

    Insert the Noid light into this fuel injector connector. You must insert the right type of Noid light into the connector. Using the wrong one will damage the female terminals inside the fuel injector connector. This will create a headache that you don't want to deal with... so be careful.

  1. 3

    When ready, stand at a safe distance from the engine but within eye-view of the Noid light and have your helper crank the car. Be careful, the car may start.

  2. 4

    The Noid light should flash On and Off the whole time the engine is being cranked or running. After noticing whatever result the Noid light produced, have your helper stop cranking the engine (or turn it off).

  3. 5

    Only one of three results are possible: a) The Noid light will flash On and Off the whole time the engine was cranking or running, or b) the Noid light did not flash On and Off at all when the engine was cranked or was running, or c) the Noid light came On and stayed brightly lit the whole time the engine was cranking or running.

  4. 6

    Repeat test steps 1 through 4 on the other 5 fuel injector connectors. This is a key step, since you'll be able to compare a BAD Noid light test result with a GOOD test result in this manner.

Interpreting The Results Of The Fuel Injector Noid Light Test

OK, in this section, we're gonna' explore in depth the three Noid light test results. Choose one of the following CASES:

CASE 1: The Noid light flashed On and Off: This result indicates that the fuel injector is receiving power and the On/Off signal from the Fuel Injection Computer. This flashing On and Off has to be compared to the results of the other fuel injector Noid light tests AND if the same, you now know beyond a shadow of a doubt that the circuits are OK.

OK, now you know that the misfire condition or rough idle is not being caused by missing fuel injector signals. Go to the end of this article to find the other Misfire Troubleshooting articles that will help you to continue diagnosing the misfire issue on your 3.8L GM vehicle.

CASE 2: The Noid light DID NOT flash On and Off: Re-test that fuel injector connector. If still no flashing On and Off, then this indicates that either power or the On/Off signal, from the PCM, is missing. This result also tells you that the fuel injector itself is not the cause of the misfire condition or Rough Idle Condition.

If all of the fuel injector connectors did not flash On and Off, when the engine was cranked, this usually indicates one of several things: a) blown fuel injector fuse, or b) a bad crankshaft position sensor, or c) an ‘open’ short in the wiring, or d) a BAD PCM, although this is rare.

CASE 3: The Noid light was lit brightly but did not flash On and Off: This result is usually a dead giveaway that the PCM is fried. In some rare cases... the circuit that feeds the fuel injector connector with the On/Off signal from the PCM is shorted to ground.