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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 3683
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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HEADLIGHTS SERVICE LIGHT COMES ON HEADLIGHT FLASHES ONLY ONE LIGHT

Customer Question

TURN ON HEADLIGHTS SERVICE LIGHT COMES ON HEADLIGHT FLASHES ONLY ONE LIGHT LIGHTS.
Submitted: 3 years ago.
Category: Chevy
Expert:  Jerry Newton replied 3 years ago.
The lights are computer controlled. The body control module is detecting a problem, and this is why the service light is coming on. The body control module might actually BE the problem, but this will require some diagnosis with a factory scan tool, and if it needs a body control module, it will have to be programmed by the dealer. For this reason, I suggest taking it to the dealer to have them diagnose and repair it for you.

This is a complex electronic system, and diagnosis shouldn't be attempted unless you have a scan tool capable of communicating with the body control module.


-Jerry
Customer: replied 3 years ago.
GO TO THE DEALER IS NOT THE ANSWER I PAID FOR. ANY IDEAS AS TO WHAT TO LOOK FOR AS THE PROBLEM.
Expert:  Jerry Newton replied 3 years ago.

I'm trying to save you some time and aggravation. Like I said, these lights are computer controlled, and the only way to accurately diagnose this is by using a scan tool.

 

If it were a matter of checking a certain connector or a certain wire, you can be sure that I'd be happy to guide you in that direction. But the simple reality is that the quickest and surest path to diagnosis starts with a scan tool, so if you don't have one of those, you are very limited with what you are able to diagnose.

 

To put it another way..... if your car rolled into my shop with that complaint, the very first thing I would do (before checking fuses or opening the hood or anything else) is grab my scan tool and plug it in. That's how vital the scan tool is on the lighting systems of this car. Couple that with the fact that the BCM's are notoriously faulty in these cars, and it makes this a no brainer: have someone diagnose it for you.

 

Feel free to opt me out if you're unhappy with my advice, but rest assured that I am trying to shoot you straight on this.

 

 

-Jerry

Customer: replied 3 years ago.
YOUR HELP IS APPRICIATED BUT IS THERE NOT A CORROSION ISSUE IN THE WIRING HARNESS OF THESE VEHICLES.
Expert:  Jerry Newton replied 3 years ago.
It depends on what part of the harness you're talking about. I wouldn't say that there is a "corrosion issue" across the board, but certainly any part of the wiring harness can be susceptible to corrosion if it has rubbed through or been modified.

When the "service vehicle soon" light comes on, that is the BCM telling you that it sees something wrong. Since the light coincides with turning on the headlights, I think it's safe to assume that the BCM sees a problem with the headlight circuit, even if the problem lies inside the BCM. There will be trouble codes stored in the BCM to help the technician track this down pretty quickly.

I'd like to give you some hints on how to do this yourself, but once again, everything leads back to the BCM. Perhaps the BCM isn't the problem, but it sure as heck is going to be part of the solution. I have a great deal of knowledge about electrical systems, body control systems, lighting systems...... and I wouldn't even THINK of trying to figure this out without a scan tool. I would be powerless without it, and you are powerless without it as well.

I know you are resistant to letting someone sort this out for you, but one of the keys of life is knowing when you're over your head. This problem is over the head of anyone that doesn't have a proper scan tool, it's just not possible to diagnose without it. You can try throwing parts at it, and you might get lucky and nail it on the first couple of tries... but that's not really what we're trying to accomplish. If I simply told you to replace the BCM, and it didn't fix the problem, you'd be angry with me for giving you bad advice. My job is to give you solid advice: my best advice is to let someone diagnose this for you. I'd give the same advice to anyone else, it's simply the best advice available.

If/When you take it in for diagnosis, the technician may very well find that there is a corrosion issue causing the problem. But without scan tool diagnostics to tell him where to look, it would just be a frustrating guessing game. Even the lighting schematic is useless if you don't know what the BCM is seeing and why it's failing to light the lights. You just have to know what's going on inside the BCM, there's no way around it.
Customer: replied 3 years ago.
I MUST INFORM YOU THAT I AM NOT POWERLESS WITHOUT A SCAN TOOL. I AQUIRED A WIRING DIAGRAM, UNPLUGED MY FRONT LIGHT HARNESS AND CHECKED MY RESISTENCES. I FOUND VERY HIGH RESISTANCE IN THE WIRE BETWEEN BOTH LOW BEAM BULBS. I PULLED OUT THE HARNESS OPENED IT UP AND FOUND TWO BADLY CORRODED SPLICES. REPAIRED THEM AND MY LIGHTS NOW WORK FINE. I GUESS IT WAS NOT OVER MY HEAD.
Customer: replied 3 years ago.
HOW DO I GET MY DEPOSIT BACK?
Expert:  Jerry Newton replied 3 years ago.

Congratulations. I don't mind being told I got it wrong, I still stand by my own advice.

 

Contact JA for a refund, or better yet, I'll contact them for you.

 

Thanks.

 

 

-Jerry

Customer: replied 3 years ago.

IT WAS GOOD ADVICE. I JUST THINK YOU WERE A LITTLE CLOSEMINDED.

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