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Discussion Starter #1
I have a 2002 Chevy Trailblazer 4.2 L6.

The engine turns over, but sometimes the headlights dim for a few seconds before the engine idle increases and stabilizes.

My car horn is sometimes very quiet if I set the alarm after turning the engine off.

A few days ago, the engine repeatedly stalled out right after starting it up. It took over a dozen key turns to get it to stay running!

I recently replaced the #3 ignition coil, so I wondered if I damaged a nearby component during that repair.

These symptoms appeared after the repair.

I have attached a screenshot of my latest Blue Driver scan report.

Do any of the codes point to a cause for the intermittent stalling, dimming lights, and quiet horn?

If not, do you have any suggestions for diagnosing the issue?

TIA for your help!
IMG_20201023_221830.jpg
 

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2004 chevy trailblazer_lt
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The first thing I would do is to check your battery cable to battery connections and make sure they are clean, and then properly tightened. Next, make sure that where the negative battery cable connects to the engine/frame is also clean and tight. There should also be a smaller ground wire that goes from the negative battery cable to a body ground. Check it and again, make sure it is clean and tight.

Now with respect to your Blue Driver report, were the codes present before the current starting difficulty appeared?
 

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2005 gmc trailblazer_ls
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Definitely electrical problem. As suggested above, check the battery terminals all grounds in a engine compartment. You mentioned that you replaced coil number 3. Disconnect it and check the pins inside and plug for broken wires. Clear the codes and try to start without number 3 plugged in. If all codes disappear except number 3 misfire you got yourself bad coil.

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Discussion Starter #4 (Edited)
Thanks, @chem_man. I'll check the ground wire connections.

Are there two? I see a smaller cable going from the negative terminal to the body, but the larger negative cable goes under a lot of other cables toward the engine block, and I can't see it very well.

The same codes are shown on an earlier Blue Driver report that I created before replacing the #3 ignition coil.

After replacing that ignition coil, the truck ran much better as first, except for the issues described above.

I didn't have any issues with stalling until over a week after that repair.
 

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Let us know the outcome. Perhaps even new coil can be defective and pulling a current down causing a dim lights.

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Discussion Starter #7
I definitely will. I'm having trouble finding all the ground wires, but I'll try again tomorrow and check the coil then 👍🏻
 

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NHinson, yes, there are two ground wires. You found where the small one goes to the body, and now you just need to follow the larger diameter one to where it connects to the engine block.

As falcon8667 said, even a new ignition coil can be defective out of the box. Especially true if it's a very inexpensive generic coil from ebay or Amazon.

I'm not really sure how to advise you on the ABS codes other than to say look things over and make sure all the wiring going to the ABS unit is intact and secure.
 

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Discussion Starter #9
Thanks, @chem_man.

It could be a defective coil, as I didn't test the new one before installing, and it's a generic part.

As for the ABS codes, my trusted mechanic told me it's likely the ABS control module, but I haven't looked into it further due to the expense 🤷🏻‍♀️

I'll check in with y'all in a day or two to let you know how it ended up.
 

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Now you know why generic parts are so inexpensive.

OK on your mechanic's take on the ABS codes.

Good Luck!
 

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Discussion Starter #11
@chem_man Both ground wires had clean, tight connections. I replaced the #3 ignition coil again, but there was no change in how the trucks starts and runs. Lights still dim and it's sluggish to start up.

The second replacement coil was from the same bunch as the first replacement, so I guess it could also be a dud.

Could it be the #3 spark plug? That was the other suggested fix on my Blue Driver report. The plugs haven't been replaced in years.

Thanks,

Nikita
 

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@falcon8667 Both ground wires had clean, tight connections. I replaced the #3 ignition coil again, but there was no change in how the trucks starts and runs. Lights still dim and it's sluggish to start up.

I checked the pins and wires on the electrical harness, but they seem fine. I plan to test the wiring harness with a multimeter if I can figure out how to do it.

The second replacement coil was from the same bunch as the first replacement, so I guess it could also be a dud.

Could it be the #3 spark plug? That was the other suggested fix on my Blue Driver report. The plugs haven't been replaced in years.

Thanks,

Nikita
 

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Discussion Starter #13
@falcon8667 Both ground wires had clean, tight connections. I replaced the #3 ignition coil again, but there was no change in how the trucks starts and runs. Lights still dim and it's sluggish to start up.

I checked the pins and wires on the electrical harness, but they seem fine. I plan to test the wiring harness with a multimeter if I can figure out how to do it.

After the first ignition coil replacement, the engine code disappeared and hasn't shown up again.

The second replacement coil was from the same bunch as the first replacement, so I guess it could also be a dud.

Could it be the #3 spark plug? That was the other suggested fix on my Blue Driver report. The plugs haven't been replaced in years.

Thanks,

Nikita
 

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Yes, it could be the number 3 spark plug. If you decide to pull the #3 plug, go ahead and pull the rest and replace them using ACDelco 41-103 iridium plugs. These engines are finicky and often do not run well on non ACDelco 41-103 plugs.

There are a couple of other things you should test before proclaiming it fixed or throwing your hands up in the air and yell "Uncle!". Get the battery load tested and while you are at it have the alternator tested to make sure it is properly charging the battery (see if it has a bad internal voltage regulator or a bad diode or two). Even if you purchased the battery 3 days ago, get it load tested to make sure it does not have a bad cell or other problem. Also, get a starter current draw test to make sure the starter is not pulling too much current and the cause of your starting problems

Go back and carefully look over your battery cables to make sure that there is no green corrosion growing under the insulation. Also look at the ends of the battery cables where they connect to the starter, frame, engine, etc., to make sure that there is no green corrosion where the cable is crimped to the connector.

The symptoms you described in your first post and in today's post strongly suggest an electrical problem and looking at the battery, alternator, starter and battery cables is indicated.
 
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