2008 3LT Canada Export

Canadian C6's have no way of disabling Automatic Headlights On at dusk (ALC). It bothers me that every time I start my C6 in the garage, on come those expensive Xenon lamps. They also seem to come on way too early at dusk - when there is still plenty of daylight.

While I was upgrading the speakers, I decided to try and defeat the ALC. I have read several posts on this, and it sounded like it would be a fairly simple task. However, when I unplugged the sunlight sensor at the center grill, I saw that there were 4 wires (not 2) involved.

After some time reading the Helms shop manual, I realized that the sunlight sensor is actually a dual sensor on C6's equipped with HVAC systems with the Auto feature. I believe this is for 3LT and 4LT options only.

The LEFT sensor is used for the headlights auto on (ACL), and the RIGHT sensor is used to detect sunlight in the passenger compartment, which can send a signal to the HVAC portion of the BCM to increase the cooling of the a/c if there is direct sunlight in the passenger compartment.

The wiring is as follows:
Left hand sun light sensor Auto Lights Control (ACL): Yellow and White
Right hand sun light sensor HVAC: Grey and Green with Black stripe

I did the following resistance checks across the ALC photocell with an ohmmeter:
Yellow and White in a dimly lit room: 15.75 Kohms
Yellow and White under a bright lamp: 8.42 Kohms
As light increases, the resistance of the photocell decreases (as it should). I cut the Yellow and White leads, and inserted a 1 Kohm resistor across them. This simulates a very bright sunny day. I’m sure that any value under 8 Kohms would work fine.
I also thought of a push button on top of the grate to allow me to choose; decided not to.

As far as the HVAC photocell:
Grey and Green with Black stripe in a dimly lit room: 54.6 Kohms
Grey and Green with Black stripe under a bright lamp: 1.5 Kohms
I left these leads intact.

Documentation for the above can be found in the Helm's manual:
4-80 Lighting schematic showing sunlight senor with Yellow and White wires for ACL
4-105 Description of sunlight sensor
4-128 Test Procedure for ACL
10-134 HVAC schematic showing sunlight sensor connected to HVAC and BCM
10-138 Describes the HVAC portion of the sun light sensor.

(Snap is the snap tab portion of the connector)


LHS Connector TOP View RHS
_____
___|SNAP|__
Yellow--| X X |---Grey
| |
White---| X X |---Green with Black stripe
|____ ______|




LHS Grille Bottom view RHS
__________
White---- | X X | ----Green with Back stripe
| |
Yellow--- | X X | ----Grey
______| SNAP |_______
| |
|________________________|


Hope this helps someone.

M.....

 

So when you turn on your headlights manually do the instrument panel lights (radio, DIC, HUD controls also light up)? I believe those are tied to the ALC sensor and if you fool it into thinking it's daytime then the IP lights won't turn on when you need them at night.

 

I think that's right too. You might have to go with the switch.

 

Interesting.

C6 is in winter storage for another couple of weeks, so I was unable to do a full test.

I would think that all the photosensor does is turn on the headlights automatically in low light conditions. I wouldn't think the IP lights would care whether I turn on the lights manually, or whether the lights are turned on automatically.

Food for thought.... I will test and get back to you.

Thanks,

M....

 

Yeah unfortunately it's a little tougher to bypass the ALC in the C6 than in other GM cars.

What I did was disconnect the photoresistor, connect a 2.2k Ohm resistor and a switch across the yellow and white leads (ALC) and left the HVAC leads open. Now you can simulate day or night. It works well, except for one quirk. If the car is already on and the switch is in the 'daytime' position and you switch it to the 'night' position it will turn on the headlights but the IP lights still won't turn on. But, if you switch it to the 'night' position before you turn the car on it will turn everything (including the IP lights) on.

 

Thanks for the input.

I have 2 questions with regards to your last post:

RE: “If the car is already on and the switch is in the 'daytime' position and you switch it to the 'night' position it will turn on the headlights but the IP lights still won't turn on.

Does this mean that everything works fine if you always leave the switch in the ‘daytime’ position? That is in essence like hardwiring the resistor in.


RE: “....left the HVAC leads open.”

Do you think there would be a problem with the BCM and a zero load across the HVAC sensor? I might try your method, but I would tend to put say a 4,700 ohm resistor across the HVAC connector. I happen to have a 4,700 resistor lying around, but I imagine any load would work fine. I also never use the Auto feature of the a/c, so I don’t really care.


Thanks again for your help.

 

It was my understanding that, for cars equipped with dual zone climate control, the left side sensor measures sunload on the driver's side and the right side sensor measures sunload on the passenger's side.

 

I don't understand your reasoning for all the concern about the HID lamps. They will out last the car, so why be concerned about them operating. With the DRL on they might just save your life some day. That's why motorcycles have had them for over 20 years. Even with DRL our cars still get run into but the percentages are low.

 

I think he's refering to the auto on HID's, not DRL's.

I have the same complaint about the HID's flashing on in the garage at each startup.

I tried the resistor in place of the ambiant light sensor and also found that the IP lights would not come on.

This is my one and only complaint about the car.

 

Well, not exactly. Let's say you start driving a little before dusk while it's still bright out and you have the switch in the daytime position. When it gets dark and you turn your headlights on manually, your IP lights will not come on. So, you try flipping the switch to the nighttime position. Even so, the IP lights still don't come on.

However, if you flip the switch to the nighttime position before you start the car, everything (headlights AND IP lights) comes on. So basically if you're going for a drive and it's gonna get dark and you need your headlights before you arrive, you need to flip the switch to nighttime before you start the car. Weird, I know, but that's just how it is. Or if you can live without your IP lights then you don't need the switch.

I haven't had any problems leaving the leads open, but the only reason I left it like that is because I was too lazy to hook up an ohmmeter to measure the resistance range. But I will probably hook up another 2.2k ohm resistor I have laying around now that you have checked out the range. I don't use the Auto feature either. Looks like we are both control freaks

 

Thanks for all the info....what I would like to do is just adjust the auto system so that the lights don't come on quite as soon. In other words, to make the lights wait until it gets a little darker before they come on. I'm going to calculate the resistance that would need to be added in parallel with the light sensitive resistor that is already there.
Also, I'm thinking that some sort of a light, attached to the garage opener light, could be set up to shine on the sensor so that the lights would not come on when starting the car, and also would not come on when pulling into the garage when arriving home. Of course it would only work if the garage opener light is still on when you start the car or drive back in. Something to think about....