Automatic Light Control Issue (Auto Lamp Control)

Tiny
B767_400
  • MEMBER
  • 1997 PONTIAC GRAND AM
  • 3.1L
  • V6
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
Hi,

Seems that I have no luck with my Grand Am.

Up to today everything was working well with my Auto Light Control.
Today I started out of my dark garage and all the exterior lamps turned on as expected.

But after driving in a pure sunlight for 10 minutes, the exterior lights were still on and did not turn off.

This is really annoying since I cannot read the time on my radio since it is dimmed for night driving.

So I stopped and turned the car off and on again without success.

Then after a few miles all of a sudden the lights turned off but after passing below a few trees (shadows) it turned it on again.

At the end it seems that it is somehow stuck to Nighttime Mode and just sparsely turns them off.

May it be the Photoresistor from the Instrument Panel?
Do I need to clean the sensor?

If yes, how can I access the sensor?

Or is there any other culprit leading to such a strange bahavior.

Thanks
Sunday, September 21st, 2025 AT 8:46 AM

17 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,591 POSTS
Yep, this is a problem with the photoresistor (ambient light sensor). I would try to find a used on on ebay. That should fix the problem.
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Sunday, September 21st, 2025 AT 9:32 AM
Tiny
B767_400
  • MEMBER
  • 36 POSTS
Thanks for your feedback.
May you also let me know how to remove the sensor?
I don't want to break anythng on my dash.
The sensor is not directly visible at the front of my dash.
Is it below the grille? Do I need to remove the grille close to the windscreen?
Any screws to remove?

This is the PN I found:
Sensor - GM (10067986)

Unfortunately not listed on Ebay right now. Is there maybe another PN from a GM vehicle I could use as well?
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Sunday, September 21st, 2025 AT 9:42 AM
Tiny
KEN L
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You are correct, the sensor is in the front of the car just behind the grill, so no need to worry about breaking anything. Here is the location, also you have the old part number here is the replacement

GM 12450121 - “Sensor Assembly, Daytime Running Lamp Ambient Light.”

Check out the images (below). Let us know what you find.
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Monday, September 22nd, 2025 AT 11:49 AM
Tiny
B767_400
  • MEMBER
  • 36 POSTS
Are you sure the part fits my 1997 GA?
I looked it up and it shows to fit a GA from 1999 to 2005.

GM (10067986) I found suits the 1996 to 1998 and this one is nowhere to find.

Please have a look at my Dash (picture attached). The sensor is not visible.

Do I need to remove the grille close to the windshield?

Also, may you have a Wiring Diagram of the ALC System?

Could I (worst case I cannot get a new sensor) disable the system?
Maybe to remove the ALC Relay in the Front Crash bar?
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Monday, September 22nd, 2025 AT 12:17 PM
Tiny
KEN L
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So the sensor is up by the grill (front bumper area) and you can use the part# I sent you which is just a newer version. If you unplug the sensor the system will be bypassed
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Monday, September 22nd, 2025 AT 1:57 PM
Tiny
B767_400
  • MEMBER
  • 36 POSTS
Thanks, but now I am a bit confused. The sensor is not within the cabin (dashboard), but outside near the grill? Do I have to open the hood to see the sensor? And then close to the two grills I can see the sensor?
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Monday, September 22nd, 2025 AT 2:11 PM
Tiny
KEN L
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Yes, yes, and yes. It should be bolted to the center core support.
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Monday, September 22nd, 2025 AT 5:26 PM
Tiny
B767_400
  • MEMBER
  • 36 POSTS
I just searched for the sensor under the hood but could not find any light sensor.

I then took my flashlight and looked for the sensor inside the cabin at the front of the dash.
Most probably I found it.
It is burried under the Windshield Defroster Vents Grill.
You can only see it if you use your flashlight from outside the windshield and point it towards the airvent grill.
See the attached picture I have taken from an Online Parts Catalogue.
It does not sit directly in the middle of the grill but a bit more to the passenger side.

If this is the sensor then I would need to remove the airvent grill and I don't know how to do it without breaking any clips.
Even if successful there is absolutely not much space to remove the sensor since it is half an inch below the grill and the windscreen is more or less directly over it.

This could become a nightmare t replace.
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Tuesday, September 23rd, 2025 AT 1:03 AM
Tiny
KEN L
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Hmm, looks like I got some bad info sorry about that. Yep you found it. It should just pop out of there, it is not held in by much. I would try to remove the vent which should help you gain access.
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Tuesday, September 23rd, 2025 AT 8:16 AM
Tiny
B767_400
  • MEMBER
  • 36 POSTS
May you also have the Wiring Diagram of the ALC System showing the sensor and relays part o the system?
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Sunday, September 28th, 2025 AT 1:54 PM
Tiny
KEN L
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Yep, here is the wiring diagrams so you can check it out and see how the system works. Check out the images (below). Please let us know what happens.
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Monday, September 29th, 2025 AT 9:25 AM
Tiny
B767_400
  • MEMBER
  • 36 POSTS
Thanks very much.
Do I understand correctly. The Instrument Cluster itself controld the ALC as well as the DRL?
There is no BCM or Light Control Module used for that in my 1997 GA?

So to check any Pins I nede to remove the Instrument Cluster (Spedo, RPM, Temp Gauge, .) Beeing able to disconnect the connector to measure any signal?
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Monday, September 29th, 2025 AT 11:18 AM
Tiny
KEN L
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That is correct, the sensor goes into the instrument cluster. What are you trying to test?
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Monday, September 29th, 2025 AT 4:29 PM
Tiny
B767_400
  • MEMBER
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I thought that it might be easier to deactivate the ALC by removing a Pin from the BCM but since it is connected directly to the Cluster I think it is not a good idea.
Removing the Cluster I guess is quite complicated.

Reason for asking is that I cannot get to the Light Sensor. It is burried too deep in the dash. I cannot get too it since the space to the windshield is marginal.

I thought maybe removing the ALC relay could also work.
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Thursday, October 9th, 2025 AT 12:01 AM
Tiny
KEN L
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Yep, that can be a tight fit but you should be able to get a small standard screwdriver to help pop it out of there? Can you upload an image close up of the sensor so I can see?
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Thursday, October 9th, 2025 AT 10:16 AM
Tiny
B767_400
  • MEMBER
  • 36 POSTS
Here is the image.
There more or less no space.
The problem is that on top of the sensor there is a round shaped plastic clip on top what has to be removed first before accessing the sensor.
And this plastic clip is approx half an inch below the vent grill.
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Sunday, October 12th, 2025 AT 9:35 AM
Tiny
KEN L
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Yes that is the vent grill, you should be able to remove the whole grill piece in one go, look for screws but if you cant find any it should just pop out of the there because it uses clips, let me know.
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Tuesday, October 14th, 2025 AT 12:09 PM

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