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GMTechBernard, Shop Foreman
Category: Buick
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Experience:  GM
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2007 Buick: the fuses, swapped the headlamp high..module..lights come

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2007 Buick LaCrosse-Every aspect of the Automatic Headlamp System works except the low beams won't come on. I checked the fuses, swapped the headlamp high-beam relay (34) with the headlamp driver module relay (35) & the symptoms didn't change. If I turn the On/Off control "on", only the parking lights come on. If I turn the switch to the "headlamps" position only the parking lights are on. The high beams function when I pull the multifunction lever toward me.
Hello! Unfortunately, because the Driver Module (HDM) operates different than a relay, its not pinned the same as a relay and therefore, you cannot swap it with a relay for diagnostic purposes. The only way to really test it is to replace it with another HDM. This is a real common issue and I wouldn't be surprised if that is all it was.
Customer: replied 6 years ago.
Both parts I swapped are called Micro-Relays in the owners manual. They are once again the Headlamp High-Beam relay (#34) & the Headlamp Driver Module relay ()#35). The markings on the two parts are identical which is why I swapped them.
In the owners manual, they are both listed under the "Micro-Relay" category, however, I assure you, the Low Beams use a completely different component as the high beams. That is why #34 is just listed as "Headlamp High Beam" and #35 is labeled as "Headlamp Driver Module". #35 is used for JUST the low beam lamps and is a sold state device. #34 is an actual relay and is used JUST for the high beams.
Customer: replied 6 years ago.

I find it hard to believe they're completely different components when they are physically identical & have the same number "15328866" on them. Like I say, when I swapped them the symptoms didn't change...the high beams still worked. If they were different then something weird should have happened. I would imagine they're both "solid state" relays...mechanical ones haven't been used for years.

Actually, relays of today still "click", they are not solid state. They still use the traditional "pull in" windings to close the contacts. Have somebody switch the high beams on and off while you keep your ear near the High Beam Relay, you will hear them in action. Take one apart some time and look inside, you will see that the more things change, the more they stay the same...

Tomorrow, I will look these up in the parts catalog, so that I can make sure the correct components are installed and we can continue from there.
Customer: replied 6 years ago.
Thanks...I'll wait for your response.
OK, so I looked the relays up in the Catalog, and they do show two separate relays.

The high beam is a standard relay (gray) and the Low Beam (called Headlamp Cut out in the catalog) is a Solid State (black).

So I went to a LaCrosse that was on the lot and confirmed what I have been saying. #34 is a gray standard relay and #35 is a black solid state.

Here is a picture of the two, side by side:

What is confusing to me, is that you stated you swapped the relays. Due to the pin configuration, this is IMPOSSIBLE and I took a picture of the pins to show you why:


So what I need you to do, is please verify that you have 100% identified the correct relays in the fuse box! If you don't mind, could you please post a picture of your fuse box so I can help you sort this out!
Customer: replied 6 years ago.

My wife has the car today...I'll do it this evening or tomorrow. In the meantime I've attached some files of what my owners manual shows. As you can see, #34 & #35 are the same physical size. I don't have a parts list to verify whether they are the exact same part but as I stated before the markings on them are identical.


Maybe my owners manual is in error or maybe I'm misunderstanding how to use it.



I have the same illustration on my computer as you do in your owners manual. Yes, they are the same dimensions but internally completely different. Take a look at it when you get home, you should have a black, relay looking component in position #35, I really don't see how a regular relay could fit in that spot (its the same size, but the pins are in different locations). Double check for me and update me when you find out.

Here is what your fuse diagram should look like:
Customer: replied 6 years ago.

I have a gray "can" in both spots. When my wife gets home I'll take a picture & send it. There has to be an easy explanation for all of this.


Thanks again!

Just checking in to see whats new...
Customer: replied 6 years ago.

You're right... I blew it!!! My apologies...sometimes I get absent-minded & this must be one of them. The same part shown in your pictures is in spot #35. Answer back & I'll be more than happy to pay you.

GMTechBernard and 3 other Buick Specialists are ready to help you
Customer: replied 6 years ago.
I might add a new relay fixed the problem. Thanks again for your help.