Bad Coil Packs are one of the more problematic ignition issues that can occur with the Chevy Trailblazer. A bad oil pack can make your Trailblazer almost un-drivable. Or it may have little effect at all on the engines ability to run. Itll get worse as they lose their ability to fire the spark plugs.
Coil Packs take the place of the distributor and coil in older vehicles. They receive instruction from the engines computer on when to fire the spark plugs. The symptoms of bad coil packs are almost the same as bad spark plugs. So much so that its actually a better idea to look at the plugs first.
Chevy Trailblazer: Bad Spark Plugs →
If you do need to replace them all, they can be somewhat pricey. It is possible to isolate which coil pack is bad by using a multimeter. Heres a great YouTube video on how to do just that. This can save you a lot of money over just replacing the whole set at one time.
Common Bad Coil Pack Symptoms: Chevy Trailblazer
There are a lot of potential symptoms related to bad coil packs in your Trailblazer. We always recommend using an OBDII scanner to pull your trouble codes if the service engine soon light is on. It can really narrow your search down. If you dont have one, your local parts store can do this for you at no charge.
Here are the most common symptoms of bad coil packs:
1. Service Engine Soon Light
The check engine light is one of the most common symptoms of bad Coil Packs. More often than not, your engines computer will be able to detect bad Coil Packs in your Trailblazer.
There are several misfire related trouble codes.
- P this trouble code indicates that there is a random misfire. A random misfire means is that a misfire is detected, but the ECM is not able to determine which one it is coming from, or the misfire is occurring randomly.
- P through P these trouble codes indicate that there is a misfire in one specific cylinder. For example, P is for a misfire in cylinder 4 in the firing order. This makes diagnosing the misfire a bit more straightforward.
There are other misfire related codes as well.
2. Acceleration isnt Normal
As you hit your Trailblazers gas pedal, the fuel and ignition systems respond. If acceleration has diminished, it should be felt. The less cylinders that your engine has, the more that one cylinder not firing properly will have an effect on engine performance.
If you have one or more bad Coil Packs, itll cause the acceleration of the Trailblazer to be weaker, and youll probably feel a jerking sensation.
3. Fuel Economy
The less efficient the combustion of your engine, the more fuel is going to be wasted. This leads to a decrease in fuel economy. When you take your vehicle in for a tune up due to decreased fuel economy, checking the ignition system in general (including the coil packs) is going to be one of the very first places that a mechanic is going to look at.
Misfiring is the most common symptom of bad Coil Packs. Anything else that you may feel is a result of the misfiring itself. The real question is, what is causing the misfire? There is more to your Trailblazers ignition system than just the coil packs. Theres also spark plugs and plug wires.
There are also non ignition related circumstances that can cause a misfire. That would include lack of fuel pressure, bad fuel injectors, or even a timing chain (or belt) that has jumped. Since there are so many reasons that a vehicle can misfire, we recommend testing for trouble codes first.
5. Rough Idling
When a Spark Plug is misfiring, it is often most pronounced at idle speed. This is because when the engine turns slower, it is easier to detect. Youll feel a rough vibration.
Conclusion: Bad Coil Packs Chevy Trailblazer
Be aware that almost all symptoms of a bad coil pack in your Trailblazer could also be other issues with the ignition system as well. Good luck diagnosing the problem! Feel free to leave a comment below if there is anything that you would like to add.
February 04, Updated: July 11, By: Abraham Torres-ArredondoArticle ID:
In this tutorial I'm going to explain how to test the ignition coils on the , , , and L Chevrolet TrailBlazer and GMC Envoy.
Testing the ignition coils, to find out if you have a defective one, isn't hard and I'll explain how to test them to find out in a step-by-step manner.
You can find this tutorial in Spanish here: Cómo Probar Las Bobinas De Encendido ( L Chevrolet TrailBlazer) (at: autotecnico-online.com).
NOTE: You can find the ignition system wiring diagram here: Ignition System Wiring Diagram ( L Chevrolet TrailBlazer).
Symptoms Of A Bad Ignition Coil
As you're already aware the ignition coil's job is to supply spark to its cylinder. This spark then ignites the air-fuel mixture within the cylinder.
Without this spark the end result is a dead cylinder that is not producing power.
So when an ignition coil fails the very first thing that you're going to notice is a misfire problem when the engine is running.
You're also going to see the check engine light lit up by a specific misfire trouble code. You'll see one or more of the following:
- P Random Cylinder Misfire.
- P Cylinder #1 Misfire.
- P Cylinder #2 Misfire.
- P Cylinder #3 Misfire.
- P Cylinder #4 Misfire.
- P Cylinder #5 Misfire.
- P Cylinder #6 Misfire.
Besides a misfire trouble code stored in your Chevrolet Trailblazer or GMC Envoy's fuel injection computer you're going to see one or more of the following symptoms:
- Bad fuel mileage.
- The check engine light flashes when the misfire is occurring.
- Rough idle.
- Lack of power as you accelerate under load.
- Engine misses (misfires) as you accelerate it's under load.
- Smell of raw fuel coming out of the tailpipe.
Ignition Coil Pin Outs
|Ignition Coil -Cyl #1|
|Ignition Coil -Cyl #2|
|Ignition Coil -Cyl #3|
|B||LT BLU||Activation Signal|
|Ignition Coil -Cyl #4|
|B||DK GRN/WHT||Activation Signal|
|Ignition Coil -Cyl #5|
|B||DK GRN||Activation Signal|
|Ignition Coil -Cyl #6|
|B||LT BLU/WHT||Activation Signal|
Where To Buy The Ignition Coil And Save
If your test results indicate that an ignition coil is defective on your L Chevrolet TrailBlazer or GMC Envoy then you should that take a look at the following links and comparison shop. I think you'll save a few bucks by buying it online:
TEST 1: Testing The Ignition Coil For Spark
Testing an ignition coil simply involves removing it from its place on the engine valve cover and attaching a spark tester to it.
Then the engine is cranked to see if the spark tester sparks. If the spark tester sparks, then you can conclude that the ignition coil is OK (not defective). You can also conclude that it's not behind the dead cylinder's misfire problem.
If the spark tester DOES NOT spark then you can conclude that the ignition coil is defective and behind the misfire problem (although it's a good idea to make sure it's getting power and an activation signal).
IMPORTANT: To get the most accurate test result from your ignition coil test you need to use a dedicated spark tester. If you don't have one and need to buy one then I recommend the HEI spark tester. You can see what this tool looks like and where to buy one here: The HEI Spark Tester (The Best Spark Tester On The Market) (at: easyautodiagnostics.com).
These are the test steps:
Remove the ignition coil from its place on the valve cover.
Connect a spark tester to the ignition coil.
Reconnect the ignition coil to its electrical connector (if you disconnected it to remove it).
Ground the spark tester with a battery jump start cable directly on the battery negative (-) terminal.
Have a helper crank the engine while you observe the spark tester.
The spark tester will do one of two things: Spark or Not Spark.
Let's take a look at what your test results mean:
CASE 1: The spark tester sparked. This is the correct and expected test result and lets you know that the ignition coil that you're testing is not defective.
This is a test result also confirms that this specific ignition coil is getting power and an activation signal from the fuel injection computer.
If the cylinder is misfiring, take a look at the following section for more testing suggestions: TEST 4: Other Common Misfire Causes.
CASE 2: The spark tester did not spark. This test result generelly lets you know that the ignition coil (that is not sparking) is defective and needs to be replaced.
Before condemning the ignition coil as defective you need to make sure that it's getting power and an activation signal. The next step is to make sure it's getting power, for this test go to: TEST 2: Making Sure The Ignition Coil Is Getting Power.
We're offline for a tune-up, we'll be up and running smoothly very soon.
In the meantime, here are some other options available:
Advance Auto Parts store
We appreciate your patience – on your next visit, use coupon code PS20 for 20% off your purchase.
We look forward to serving you,
The Advance Team
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