: Twilight sentinel question

01-04-09, 08:53 PM
Twilight sentinel in my 89 Brougham is currently inoperable. Anyone else ever have to fix theirs? Wondering what the most common problems would be. Photo cell? Or maybe sentinel control (where is it located?). Lights work manually so no biggie but it just bugs me when things dont work the way they should on my caddie. Any info appreciated.

01-05-09, 12:05 AM
I have a factory service manual for an 89 Brougham, and to find the fault in the sentinel system is very tedious. There are four pages of problem trees relating to the sentinel system and there is no way of coherently explaining it.

If you want to rule out the photocell, then disconnect it an turn the ignition on. If all of the lights come on within 60 seconds, replace the photocell.

01-05-09, 05:42 PM
Ok, it was the photocell. Greatly appreciate the info. Now where can I get one? Will I have to get one from a salvage yard or can you order these things from GM or even a parts store. Thanks again.

01-06-09, 12:01 AM
According to my manual, the photocell is accessed by removing the instrument panel top cover. You remove it by pulling it straight out of its holder and reinstall it by pressing it straight back into the holder. You should be able to find the photocell at any AC Delco parts distributor.

And being that diagnosing and repairing this system, and other more crucial systems is such a detailed oriented and tedious task, I suggest you consider one of these service manuals (http://shop.ebay.com/items/__1989-cadillac-service-manual_W0QQQ5ftrkparmsZ72Q253A1205Q257C66Q253A2Q25 7C65Q253A12Q257C39Q253A1QQ_dmptZMotorsQ5fManualsQ5 fLiteratureQQ_fromfsbZQQ_trksidZp3286Q2ec0Q2em14QQ _sopZ15QQ_scZ1).

01-06-09, 08:36 AM
The photocell replacement is very easy. Just change it like a light bulb. The only other concern is calibration. Once you change the photocell, you may notice that it comes on earlier or later than before. Under the dash on the driver side is a box with a calibration screw. Just follow the wiring from the dash switch to it. A small screwdriver will do the trick. I think each notch is about 5 minutes. Also keep in mind that since the sensor is under the dash peeking through a grill, that the lights will always come on earlier in the winter months because the sun is closer to the horizon.

01-12-09, 12:55 AM
In my manual it recommends that both should be replaced as a set. The photo cell and the controller box.

01-12-09, 03:21 AM
Replaced the photocell with one from radio shack. GM wanted 45 bucks for the whole photocell assembly. I paid 2.99 for 5 assorted size photocells and just removed the original from the housing and replaced it with the largest one in the pack. It works fine but I may need to calibrate it. Thanks for all the great info.

01-12-09, 07:25 AM
If you replace as a set, the calibration is already done for you. I have always gone to the junkyard and grabbed one. This is getting more difficult as most yards now do not allow customers to pull thei own parts.

12-26-09, 07:36 PM
Does anyone know if the twilight system has to be reset if the vehicle was stored without a battery in it. Mine was working before and now is not. i can't seem to find any diagnostic info.

12-26-09, 09:33 PM
I don't think it has to be reset. mine was sitting in my brother -in- laws driveway for to years with a dead battery before i took it off his hands. put a new battery in and it worked fine, except for the occasional not shutting off after you turn off the car.

12-27-09, 02:19 AM
Nope. Try disconnecting the battery agian.

03-14-10, 08:33 PM
The Twilight Sentinal in my 1988 uses a CdS photo resistor. It has gone out of range too low (5K Ohm when light to 15K dark). This makes the BCM think it is always light.

After some playing with a variable resistor plugged in it's place and a volt meter I find it should switch to day at 33K Ohms and back to night at 45K Ohms. I found a compatible part at digikey DOT com. Here is the data sheet : advancedphotonix DOT com/ap_products/pdfs/PDV-P9004.pdf . It is listed as a 27K to 60K Ohm sensor. (note the form won't let me post web addresses, so I used DOT)

Note: the ECM/BCM readouts for "Body data" for the photo sensor reads very close to K Ohms and the numbers are: switch to day at about 33 and night at about 45. This has a delay at the switch points.

It is a $1.75 part and should work..... I will try it anyway....not thrilled with $45 for the factory part!