How do I go about testing my ambient light sensor with a multimeter?

[Forceofaqua]

I would assume this is a simple thing to do, but my multi meter readings are simply not changing. I am testing resistance between the two prongs with light and no light and nothing changes. Can someone do this test to show me what the sensor should be reading, or tell me how to test it?

The issue I'm running into is that none of my running lights are working, and I've tested continuity across all brown wires and the fuse box. The fuse is also not blown. The sensor is the last piece to test, and its brand new out of the box.

Secondary question, is there an easy way to bypass the sensor to force the daytime running lights on? I'd like to test if all the wiring and the dash light up.

 

[Ark :D]

Cobalt DRL's are on full-time, with or without the ambient light sensor. All the sensor does is trigger the circuit to pass through a higher-resistance wire, thus dimming the DRL's. The sensor has nothing to do with your running lights/brown wires.

 

[Forceofaqua]

Ahh well that’s kinda good news. I’ve been going throw a crazy person rabbit hole figuring out the DRLs, and I was convinced it was the sensor. Thanks!

 

[Rauq]

The 2005-06 Cobalts run the front turn signal as the DRL. The 2007+ Cobalts run the high beams at half voltage for the DRL and use a separate DRL fuse. I don't recall if unplugging the sensor makes the car think it's day or night or neither, but assuming the sensor isn't bad, you can force the DRLs on by putting a flashlight in front of the sensor for like 30 seconds.

 

[Ark :D]

Apologies on not realizing 05-06 was different than 07+. Will try to cut down on bad information going forward.

 

[Rauq]

No worries, we all pick up our quirks of information through our build processes. I have a couple of your posts bookmarked from things you've done that I either have duplicated or plan to duplicate!

If anyone's more electrically inclined than I am and wants to correct me if I'm wrong, I believe the ambient light sensor is a photodiode. I think if you set your multimeter to read current (mA range) and hit the sensor with a flashlight you should get a change. Not sure if polarity matters there.

 

[Desert Sasqwatch]

Correct, it should create a small current. The anode will become more positive than the cathode when exposed to light. Since the sensor is not marked for polarity, hooking up the meter will not really matter, you will either read a positive or negative amperage value - and it will be small probably in the 10s of mA.

 

[Goblinfanclub1234]

what donor car do you have? Based on what Rauq said,

The 2005-06 run the front turn signal as the DRL - does this mean for the 05-06 donor goblins the mirror lights light up for DRL? If the turn signal wire goes the mirror then you wont get any DRL out of the headlights. maybe this is the problem?

2007+ you could measure voltage on the high beam wire, white wire, with the car running. it should be around 6-7 volts maybe?

I think if there is zero voltage on your appropriate DRL wire then I would look at the light switch on the steering column. are you troubleshooting with the switch set to "auto"?

 

[ctuinstra]

I've measured the ambient light sensor before in the circuit. It's a 5v circuit with dark being 5v signal and the more light, the more it goes to close to 0 volts. At about 2.5v, it switches from between day and night.

 

[Desert Sasqwatch]

So it's a photoresistive device and not a photodiode then. This would likely consist of a photocell and a bias circuit. Photocells have higher resistance in the dark and become more conductive in light.

And I think we have hijacked this thread long enough.