Sun Load Sensor and Ambient Light sensors
#1
Sun Load Sensor and Ambient Light sensors
I'm getting conflicting answers when I search the forum about what is in the center of my defrost vent. I have a 1999 Trailblazer with the electronic HVAC (set a temp) controls. One post says that it's the ambient light sensor (GM 12450120) for the automatic headlights, another says it's the Sun Load sensor (GM 13578464). I looked over at the passenger side speaker cover and there's something there that's been pushed down and is moving around, probably part of my DRL issues if it's the ambient light sensor. No OnStar until 2000 so it's not a microphone. I'm prepping the rig so the wife can drive it cross country and she has higher standards than I do when it comes to things like driving lights and HVAC controls. I'm used to dim lights and using the window to regulating temperatures and she's used to HID and computer controlled to an exact temperature. I get 23 year old Blazer and a 3/4 ton work truck, she gets a new Charger, happy wife and all that, right? The Charger is going to be shipped and she won't drive the quad cab long bed 3/4 ton for some strange reason.
#2
I'm getting conflicting answers when I search the forum about what is in the center of my defrost vent. I have a 1999 Trailblazer with the electronic HVAC (set a temp) controls. One post says that it's the ambient light sensor (GM 12450120) for the automatic headlights, another says it's the Sun Load sensor (GM 13578464). I looked over at the passenger side speaker cover and there's something there that's been pushed down and is moving around, probably part of my DRL issues if it's the ambient light sensor. No OnStar until 2000 so it's not a microphone. I'm prepping the rig so the wife can drive it cross country and she has higher standards than I do when it comes to things like driving lights and HVAC controls. I'm used to dim lights and using the window to regulating temperatures and she's used to HID and computer controlled to an exact temperature. I get 23 year old Blazer and a 3/4 ton work truck, she gets a new Charger, happy wife and all that, right? The Charger is going to be shipped and she won't drive the quad cab long bed 3/4 ton for some strange reason.
#3
#4
That's fantastic! I'm a little confused on the Ambient being in the upper LH of the instrument panel though. Could that be the cutout in the dash speaker cover? There's nothing topside on the driver's side. Could it be the 'Left Hand' while facing the truck from the front? Either way, it looks like I should probably start looking around for a factory service manual if I plan on keeping it (and I do, this little $600 dog hauler has won me over these past several years despite it's quirks). Thank you for answering!
I don't know what I would have done without my service manual. Be warned though, some of the procedures assume little things like the engine being out of the vehicle or that you have access to all the special tools. LOL I have a hard copy. It comes in three volumes! I got it off eBay ages ago.
#6
#7
While I'm not looking at a Trailblazer manual, from what I see B2647 is AMBIENT LIGHT SENSOR LOW. In GM speak "low" = ground. Based off your symptoms in another post, it would make me think that you either have a short to ground or a problem with your BCM. Since I also saw these problems started happening after you had your dash apart, combined with your symptoms I would really lean towards a short more than a BCM problem. Logic: Your trouble code combined with the fact your door circuitry is finding a path to complete the circuit when it shouldn't. I'd recommend you purchase a subscription for your truck's service manual at https://www.alldata.com This will not only provide you with trouble shooting steps for the code, but will also provide color wire diagrams you can follow.
If you don't have already, I'd get a DVOM and a test lamp.
EDIT: Looks like Christine and I were responding at the same time. Following the steps she provided should point you in the right direction.
If you don't have already, I'd get a DVOM and a test lamp.
EDIT: Looks like Christine and I were responding at the same time. Following the steps she provided should point you in the right direction.
Last edited by rockp2; 02-01-2023 at 07:38 PM.
#8
I scanned this for you (attached). This is the diagnostic list for this error. Maybe it will help you track down the problem. Maybe it is a bad connector or bad wire. The circuit looks pretty simple. Just be careful to ground yourself to discharge any static on your hands and on your multimeter before touching the leads to the BCM.
#9
While I'm not looking at a Trailblazer manual, from what I see B2647 is AMBIENT LIGHT SENSOR LOW. In GM speak "low" = ground. Based off your symptoms in another post, it would make me think that you either have a short to ground or a problem with your BCM. Since I also saw these problems started happening after you had your dash apart, combined with your symptoms I would really lean towards a short more than a BCM problem. Logic: Your trouble code combined with the fact your door circuitry is finding a path to complete the circuit when it shouldn't. I'd recommend you purchase a subscription for your truck's service manual at https://www.alldata.com This will not only provide you with trouble shooting steps for the code, but will also provide color wire diagrams you can follow.
If you don't have already, I'd get a DVOM and a test lamp.
EDIT: Looks like Christine and I were responding at the same time. Following the steps she provided should point you in the right direction.
If you don't have already, I'd get a DVOM and a test lamp.
EDIT: Looks like Christine and I were responding at the same time. Following the steps she provided should point you in the right direction.
#10
So i finally got my digital volt meter in (I know it took awhile but I'm cheap and ordered off Amazon) and went to check my bcm and... should there be an open port? From driver side view looking in from bottom to top its: open, light blue, brown. Please tell me that's for something like a sunroof or factory amplifier or basically ANYTHING I don't have! I am 99.9% sure that I didn't miss any connections when I reinstalled the dash (heater core replacement) but that empty plug has me worried now. I don't WANT to pull the dash again but if that's what happened, I'm going to kick myself.
Say it ain't so!
Say it ain't so!