I have a 2003 LS MC. On occasion, all of the lights will just turn off. Doesn't matter if I leave them in daytime mode or if I pull the head light plunger out to keep them on all of the time. No big deal, all I have to do is turn them on and off and it resets itself. What would be causing this issue? A ground maybe?

 

Do they go completely off or do they dim really low?
Dimming could be the headlight switch itself or possibly the light sensor on the dash.
Off completely could be a bad ground I suppose. I'd have to look at the wiring diagrams to see if all those systems share a common ground... but if it was a ground issue turning them off and back on would be less likely to resolve the issue.

My money is on the light switch frankly or ambient light sensor.
Both the ambient light sensor and light switch feed into the BCM and could cause these issues.
Are there any other funky things going on with the vehicle? gauges not working properly, idiot lights going off, service engine soon messages, keyless entry not working, etc? Some of these things might seem unrelated but might be useful to know.

From what I've been able to research the ambient light sensor is relatively cheap and easy to change.

 

The only other thing that happens, is the e-brake light stays on after I have started the car and released it. It will shut off after I turn the car off and turn it on. Also, the high-beam indicator light stays on after I disengage them. Once again, it goes away when I shut the car off and turn it on.

Now, I think I have a computer issue though. Sometimes the transmission will shift hard and sometimes it will run like a champ. Very inconsistent.

 

My understanding is the transmission stuff is more controlled by the PCM and the BCM controls a lot of the convienence features, security, etc.

is it just the indicators which stay on or are the high beams actually on?
The reason I ask is the dimmer switch turns on the high beams and also has a line which communicates to the BCM that they're on. The BCM then communicates to the class 2 data system which also communicates to the instrument cluster.

The parking break also is ground side switched and runs into the BCM. So if the instrument cluster has the brake light on the BCM is telling the cluster that is pressed and grounded and to turn that light on.

With the illumination, the high beam indicator issue and the brake indicator issue I'm more inclined to call it a failing BCM or a ground issue with the BCM itself. The BCM is a known pattern failure on these vehicles although typically the signs of that are the radio is in locked mode, the keyless entry doesn't work, etc.

Amazon sells new AC Delco BCMs for $120 and most oriely auto parts locations can get a reman A1Cardone BCM for about $100 after core exchange. Personally for the price difference I chose to go new when I needed to replace one.