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Dash light problem is back


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Last fall, I started having a problem where my car would go into what I call "daylight driving mode" (dash lights off except for LED displays on the radio, AC controls, odometer, and DIC; headlights on at only partial strength; and no interior lights when I park the car) while driving at night. The car would not go back into nighttime driving mode unless I parked it and shut it off for several minutes, which seemed to allow the system to reset. After a lot of experimentation, I finally found that I could control the system manually by covering the ambient light sensor on the dashboard with black electricians' tape to make the car think it was always dark outside, keeping the twilight sentinel turned off, and keeping the fog lamps turned on so the "headlamps suggested" reminder would not constantly appear on the DIC.

This solution worked fine until a few weeks ago. Now, it spontaneously goes into "daylight driving mode" whenever I drive with the headlights on for more than about 10 or 15 minutes. This is very annoying, not to mention dangerous. Any insights or suggestions for a fix would be greatly appreciated.

Edited by human

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  • 4 weeks later...

Things are going from bad to worse. I am now lucky if the dash lights stay on for even three or four minutes. Most of the time when I'm driving at night, I cannot see my speedometer. HELP!

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In reference to your second post, when this happens your headlights go into "daytime running light mode" also?? If that is the case, seeing your speedometer is not the only problem you have, your lights are in DRL mode making it hard to see, correct?

It seems that the sensor you are covering is 'sensing' that its daytime or sunny out and it seems that it finally died and it is out of calibration regardless of whether you cover it or not. I would try replacing that sensor its called the "twilight photocell" according to my manual

The 'air vent louver' pops out, use a credit to gently pop it out, start on the wings and work inward gently, pop the speaker out on the sides, don't force, move in from the sides and lift the speaker area, so as not to crack it. There are two sensors one you want is blue

If you buy a new one, and have an OHM meter, please report what the resistance is of a new sensor, I could not find it in the manual and that would be good to know

I had the opposite problem, my lights stayed on all the time, as the sensor thought it was DARK out, from what I understand the sensors drift, but given the heat they experience through the windshield, I am not surprised

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks for your reply. Is this photocell something I can pick up somewhere like AutoZone or do I need to go to a dealership? Is there a part number I should be looking for?

Getting the air louver out isn't a problem. The dash is kind of warped and the louver isn't firmly seated. I can just lift it up to get to the underside. So taking the speaker out will give me access to where the photocell plugs in?

I'll post an update once I get the part and install it.

In reference to your second post, when this happens your headlights go into "daytime running light mode" also?? If that is the case, seeing your speedometer is not the only problem you have, your lights are in DRL mode making it hard to see, correct?

It seems that the sensor you are covering is 'sensing' that its daytime or sunny out and it seems that it finally died and it is out of calibration regardless of whether you cover it or not. I would try replacing that sensor its called the "twilight photocell" according to my manual

The 'air vent louver' pops out, use a credit to gently pop it out, start on the wings and work inward gently, pop the speaker out on the sides, don't force, move in from the sides and lift the speaker area, so as not to crack it. There are two sensors one you want is blue

If you buy a new one, and have an OHM meter, please report what the resistance is of a new sensor, I could not find it in the manual and that would be good to know

I had the opposite problem, my lights stayed on all the time, as the sensor thought it was DARK out, from what I understand the sensors drift, but given the heat they experience through the windshield, I am not surprised

The secret to flying is to throw yourself at the ground--and miss!

--Douglas Adams Life, The Universe, and Everything

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  • 3 weeks later...

Well, I finally had some time this morning to sit in the car when it wasn't too hot and fiddle with the photo cell. Actually, I was waiting for someone in a parking lot and had nothing better to do. I found that it's really easy to remove the photo cell. Just lift up the defroster vent (my dash is a little warped so it doesn't seat properly, making access even easier), twist the photo cell socket from underneath, and then pull the button-sized sensor out of the socket. The best part is that with the photo cell removed, the lights work almost normally. I can turn them on manually with the pull switch and the dash lights and exterior lights come on--and stay on! I can also turn the lights on with the Twilight Sentinel slider, and everything works just fine. The lights will even time themselves out after the selected interval once I turn the engine off and exit the car. Of course, without the photo cell, they won't come on automatically while I'm driving, but I can live with that for now, especially considering how broke I am at the moment. Anybody know of a compelling reason not to leave the photo cell out for an extended period of time?

I'm really not in any hurry to shell out between $30 and $60 for that for that stupid little part. I can't believe it retails for $56! The best price I found online was from gmpartsdirect.com, which is the mail order operation for the parts department at Flow Motor Co. in Winston-Salem, NC. They wanted $31 plus shipping—and then throw in sales tax on top of that, since I'm also an NC resident. I haven't had the time to look search junkyards yet, but I do know where there's a late '90s-vintage Buick Park Avenue that appears to be in the process of being parted out. I'm thinking that may be a potential source for a cheap used sensor. Anybody know if the part would be compatible with a Caddy? I'm thinking the odds might be in my favor on that one.

Anyway, thanks for all your sage advice and I'll keep you updated.

Edited by human

The secret to flying is to throw yourself at the ground--and miss!

--Douglas Adams Life, The Universe, and Everything

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  • 2 weeks later...

It's been almost two weeks since I pulled the Twilight Photocell and everything is still working fine as a manual system. I am, however, getting a trouble code, IPC B2419, which translates to English as "Twilight Photocell Circuit Problem". I find it a little odd that with a failed Twilight Photocell in place, I got no error codes. Another little minor quirk is that with the fog lamps turned off, I get the message "Headlamps Suggested" on the DIC. I used to get the same message when I was covering the defective photocell with electrical tape. No big deal; I just leave the fog lamps on.

The secret to flying is to throw yourself at the ground--and miss!

--Douglas Adams Life, The Universe, and Everything

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I am not 100% sure, but would it not be possible to bypass the photocell (without removing it) by just turning the twilight sentinel to OFF, and then use the normal light switch to turn the lights on and off? I think that the light switch will also regulate weather the speedometer illumination is on or of if the twilight sentinel is set to off.

Be advised that with daytime running lights, the tail lamps are turned off, so it's not just the headlights dimming and instrument illumination disappearing. Maybe you already new this, but I thought it's worth mentioning anyway... The fix is of course to manually turn on the lights by pulling out the knob.

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As I mentioned, your photocell has DRIFTED, that is why it is not regulating the turnon turnoff properly, when you UNPLUG it the system detects its UNPLUGED, that is why you get the code. IT must be plugged in. If the photocell it too much, go to a scrap yard and get one off a wreck

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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This dash light phenomenon was happening regardless of whether the Twilight Sentinel was turned on or off, although it was generally worse when it was on. When I had the electrical tape over the photocell, I was turning the lights on and off manually with the pull switch on the dash, and for five months or so it worked just fine like that. By late spring, it started going back into daylight mode on its own, even when the lights were turned on manually. Removing the photocell has restored the level of function I had when I first started covering it with electrical tape last fall.

At some point I will likely look for a photocell on a boneyard; but for now, the system is functioning acceptably. My major concern for the immediate term is whether the lack of a photocell is going to cause any further damage.

I am not 100% sure, but would it not be possible to bypass the photocell (without removing it) by just turning the twilight sentinel to OFF, and then use the normal light switch to turn the lights on and off? I think that the light switch will also regulate weather the speedometer illumination is on or of if the twilight sentinel is set to off.

Be advised that with daytime running lights, the tail lamps are turned off, so it's not just the headlights dimming and instrument illumination disappearing. Maybe you already new this, but I thought it's worth mentioning anyway... The fix is of course to manually turn on the lights by pulling out the knob.

Edited by human

The secret to flying is to throw yourself at the ground--and miss!

--Douglas Adams Life, The Universe, and Everything

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This dash light phenomenon was happening regardless of whether the Twilight Sentinel was turned on or off, although it was generally worse when it was on. When I had the electrical tape over the photocell, I was turning the lights on and off manually with the pull switch on the dash, and for five months or so it worked just fine like that. By late spring, it started going back into daylight mode on its own, even when the lights were turned on manually. Removing the photocell has restored the level of function I had when I first started covering it with electrical tape last fall.

At some point I will likely look for a photocell on a boneyard; but for now, the system is functioning acceptably. My major concern for the immediate term is whether the lack of a photocell is going to cause any further damage.

I don't see how it could cause any damage to anything.

It is just the photocell unplugged.

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NO, the pulled photocell is NOT causing damage its just throwing a code.... and AGAIN, your CELL did NOT fail, it drifted.

You should purchase a factory service manual and follow the diagnostic tree for this problem

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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  • 9 years later...

The best source these days is probably a boneyard. The same sensor was used in several different GM models of that era. Might as well grab two or three in hopes of getting at least one good one. I simply unplugged my car's sensor from its socket and everything worked just fine as a manual system for the rest of the time I owned the car. I ended up selling it early in 2011.

The secret to flying is to throw yourself at the ground--and miss!

--Douglas Adams Life, The Universe, and Everything

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