Guest Kitskaboodle Posted November 15, 2011 Share Posted November 15, 2011 Hi all, I would like to disable this feature because it comes on when it's relatively light outside. (I am starting to dislike it's judgement calls) Is there a simple way to disconnect it? Does it have it's own fuse?Thanks, Kit Link to comment Share on other sites More sharing options...
NCReatta Posted November 15, 2011 Share Posted November 15, 2011 You just have to open up the IPC and bust the bulb with a pair of needle use pliers or something. Link to comment Share on other sites More sharing options...
padgett Posted November 15, 2011 Share Posted November 15, 2011 Many use electrical tape. This is a 90-91 "feature". Can think of better uses for an indicator. Do think it should go out if side/tail/fog lights are on. Link to comment Share on other sites More sharing options...
Guest Mc_Reatta Posted November 15, 2011 Share Posted November 15, 2011 It is not easily defeated as it is a function controlled by the BCM in response to the amount of light hitting the photocell in the dash. As it is needed to allow for the dimming of the dash lights as well, so the photocell function can't be disabled.When the software in the BCM program is finally documented, this function will be able to be done away with. Link to comment Share on other sites More sharing options...
jonlabree Posted November 15, 2011 Share Posted November 15, 2011 I suppose you could mount a small LED in front of the sensor. Link to comment Share on other sites More sharing options...
KDirk Posted November 15, 2011 Share Posted November 15, 2011 It has occurred to me that perhaps it is triggered prematurely due to deterioration of the photocell. I have the same problem on my 91, and if the twilight sentinel is on, the headlamps come on well before it is dark enough to justify their use. Since I did not own the car when new, I have no idea if it always behaved this way, or if the darkness needed to trigger this feature has decreased over time due to a failing photocell. Anyone here care to comment on this theory? If the threshold for activation of twilight sentinel/headlamp suggested lamp was always this premature, then somebody at GM screwed up the programming in the BCM PROM badly. I suppose if the bytes in the BCM PROM that control the activation level could be found, it could be adjusted to wait until a greater level of darkness before it kicked on. This is really the correct fix, provided the issue is not just the photocell acting stupid.My 95 Deville has twilight sentinel, and works as I would expect: headlamps do not come on in late afternoon shadows, when driving under a long line of tree cover, or on overcast days. Oddly enough, a headlamps suggested warning is not implemented on that car. The 96 and later Deville/Eldo/Seville do have a headlamp suggested message on the cluster. I think I need a new photocell anyway, since the IPC does not seem to dim at all when the headlamps are on. Yet another nuisance item I need to address. Will it ever end?KDirk Link to comment Share on other sites More sharing options...
padgett Posted November 15, 2011 Share Posted November 15, 2011 Getting the "Headlights Suggested" indicates the photocell is working. If not dimming you may have another issue. Link to comment Share on other sites More sharing options...
Ronnie Posted November 16, 2011 Share Posted November 16, 2011 The point where the BCM dims the dash lights (and probably when the Headlights Suggested message is displayed) can be changed by increasing or reducing the resistance in the photocell circuit. When I got my car the photocell was working but the readings were out of range so I was getting a B119 code and the lights didn't dim at the correct time so.... To prevent getting a code B119, I installed a resistor (either 200k or 2 meg, I have forgot) between the BCM connector 3D8 and the BCM ground terminal. That put the the photocell circuit resistance in the correct range to make the BCM happy and dim the lights when it is getting dark. Has worked good since. I added the resistor because I didn't want to risk breaking the dash to replace the photocell.Maybe adding a resisistor would be an easy solution to the Headlights Suggested message coming on at the wrong time. Link to comment Share on other sites More sharing options...
KDirk Posted November 16, 2011 Share Posted November 16, 2011 Ronnie has just expanded on what I was referring to, that the photocell works, but does not read correctly. This seems to result in the system erring on the side of reading darker than it really is (photocell triggers twilight output well before it should, based on the outside light level). Ronnie's fix is also ingeniously simple, much more so than my idea of patching the BCM PROM. I rather suspect that the photocell is out of calibration due to chemical changes in the CDS in many cars of this vintage (88-91). Many here have posted about problems with the photocell and it's related systems since I first joined the forum in 2007. I would not be surprised that they are degrading after 20+ years of full-on sunlight and high heat exposure. I also find it difficult to believe that GM programmed it to be so sensitive to begin with, seems like there has to be some other type of issue that is causing this for so many Reatta owners. The photocell is the logical suspect.KDirk Link to comment Share on other sites More sharing options...
padgett Posted November 16, 2011 Share Posted November 16, 2011 5/50 ? Link to comment Share on other sites More sharing options...
Guest Mc_Reatta Posted November 16, 2011 Share Posted November 16, 2011 Performance ot the photocell may well be degraded from age and I would expect from dirt and dust falling down onto the surface of the cell. Too bad it's so hard to get to just to try to clean its window.Its performance should be able to be determined by looking at the value of BD44 in diagnostics. Display is a % between 0 and 100. The more light it sees, the lower the number. In twilight mode, lights would turn on at 90 (4 volts) and turn off at 30 (2 volts).FSM doesn't say where the headlights suggested warning gets triggered on or off in this range.Suppose the next step is for a gathering of readings from individuals as to what readings do they see in bright sunlight and when the warning comes on to evaluate the performance of the photocell to see how a normal one behaves, and how a weak one performs. Link to comment Share on other sites More sharing options...
Guest Kitskaboodle Posted November 16, 2011 Share Posted November 16, 2011 I should have mentioned that I replaced my twilight sensor about 2 years ago. From what I'm reading though it may not be a photocell issue but rather the amount of voltage getting to the sensor, correct?Kit Link to comment Share on other sites More sharing options...
Guest Mc_Reatta Posted November 16, 2011 Share Posted November 16, 2011 The BCM supplies a 5 volt reference voltage to the cell. The photocell is a variable resistor. The other side of the cell is connected to ground. The more light it is exposed to, the lower its resistance and more of the 5 volt reference is bled off to ground and the BCM senses this. Conversely, in the dark the resistance stays high, and little of the 5 volts is lost.Where did you find your replacement photocell? Was it an exact match to the original part? If the replacement cell had different operating properties, it would affect the voltage seen by the BCM at a specific light level and may be the cause of the warning coming on in brighter conditions than expected. Link to comment Share on other sites More sharing options...
harry yarnell Posted November 16, 2011 Share Posted November 16, 2011 While I'm at my local junkyard, I harvest all the photocells I can get off of Buicks and Cadillac's of the period. Bring them back to the bench and check thier resistance with/without light. I forget what numbers I consider good (will have to check if anyone's interested), but the wider the swing of resistance were the one's that got put in stock.Maybe 60% of the lot would be a good acceptance. Link to comment Share on other sites More sharing options...
KDirk Posted November 16, 2011 Share Posted November 16, 2011 MC,Very good observations on your part regarding the functioning of the photocell. FWIW, I believe the headlamps suggested warning is triggered from the same BCM signal (or at least at the same level of photocell feedback) as the twilight sentinel would activate (on 1991's). My logic here is that if I have the twilight sentinel on, I obviously never see the headlamps suggested warning. If T/S is off, the warning lamp comes on when the headlamps would otherwise activate if T/S was turned on. So, at least on the 1991, the warning lamp shows instead of the headlamps turning on automatically when T/S is disabled by the slider on the headlamp switch. KDirk Link to comment Share on other sites More sharing options...
Guest Mc_Reatta Posted November 17, 2011 Share Posted November 17, 2011 The only other magic number I could discover for the photocell control was the value of BD44 where the IP dimming function is invoked. That value is 74. That's the only one that matters to none 90's owners.If someone with a 90 or 91 wants to cover up the photocell until the headlight suggestion comes on and then reads the value of BD44, then we will know what the magic number is for that.Of course, this does nothing to figure out what outside brightness level is needed for a given photocell to report that number to the BCM. It would however give an indication of what the resistance value of the photocell needs to be which could be used as a starting point to figure out what resistor value might be used to supplement the circuit to modify it to turn the warning on later. Link to comment Share on other sites More sharing options...
Guest Richard D Posted November 17, 2011 Share Posted November 17, 2011 Just a guess but you might take a long soft brush and try to clean the dust and stuff of the top of the cell throught the dash top and see if that makes any difference. Link to comment Share on other sites More sharing options...
Guest Squire Tom Posted November 20, 2011 Share Posted November 20, 2011 slide the sentinel switch to OFF. Link to comment Share on other sites More sharing options...
harry yarnell Posted November 20, 2011 Share Posted November 20, 2011 Will that do it? I thought the whole idea of HS was to eliminate the pesky manual application of the headlight switch. Link to comment Share on other sites More sharing options...
Guest Kitskaboodle Posted November 21, 2011 Share Posted November 21, 2011 The BCM supplies a 5 volt reference voltage to the cell. The photocell is a variable resistor. The other side of the cell is connected to ground. The more light it is exposed to, the lower its resistance and more of the 5 volt reference is bled off to ground and the BCM senses this. Conversely, in the dark the resistance stays high, and little of the 5 volts is lost.Where did you find your replacement photocell? Was it an exact match to the original part? If the replacement cell had different operating properties, it would affect the voltage seen by the BCM at a specific light level and may be the cause of the warning coming on in brighter conditions than expected.To answer your question, I know I purchased a NEW one but I do not remember the brand. I will need to look through old receipts. In addition, I had a mechanic install it. That's back when I could afford to hire someone to work on all my cars. 'Kit Link to comment Share on other sites More sharing options...
Guest Squire Tom Posted November 22, 2011 Share Posted November 22, 2011 how hard was it for your grand father to turn the headlights on and off? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now