I don't know how much expertise anyone would have on the last-Gen GM minivans, but being GM, it probably doesn't change across the line. We have a 2006 Chevy Uplander with a BRAKE red warning light.

Some background: It's a daily driver with (I'm pretty sure) over 150,000 mi on it. The check engine light has been on for a while (gas cap that can't be fixed as far as we know), as well as the ABS ($700 or just go without ABS, which we know how to do). Its daily commute was just increased recently by maybe 15-20 minutes.

The red "BRAKE" light (that normally comes on when you leave the parking brake on) comes on sometimes while just driving normally. It stays lit and the DIC displays "SERVICE BRAKE SYSTEM". We and a Jiffy Lube have checked the brake fluid, and there is always plenty. I assume this is some sort of sensor problem, then. Any ideas on what I would be looking for? Something that tells the computer if the parking brake is on or not? Brake fluid sensor? Replace pads or rotors? Any ideas or help are appreciated. Thanks!

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brownishSLE
"Family heirloom" Brown-on-brown 2000 SLE

It's not winter anymore.
I'll get a new photo up
soon.

Why can't the gas cap just be replaced to fix the seal and thus shut off the check engine light ?
Are you just assuming that the check engine light is on because of the gas cap because you know that this sometimes happens with cars or someone told you that that happens?
Not meaning to insult you, but I have no way to know whether or not you know that check engine light will come on to tell you there's a problem with any of a number of things, not just faulty sealing of gas caps.
Autozone and other automotive chain stores will often check your vehicle for codes for free or you can buy a scan tool and check them for yourself.

For the brake warning light issue......
The first thing to know is that looking at the fluid level without removing the cover of the master cylinder may give you (and everyone else) a false indication that the reservoir is full, even thought the fluid is low.
Over the years, a dirt line forms and although the reservoir appears to be full, it isn't.
Get a flashlight, remove the cap and look to see where the fluid level is.
It should be be higher than the low level.

It's always a good idea to check all 4 wheels for brake wear and/or leaks before a minor problem becomes a major problem.
Road salts are known to rust out the metal brake lines and a small leak can rapidly become a very serious problem.
One or more bad seals within the brake system and/or external leaks will also illuminate the brake warning light.
In addition to the parking brake, leaks or a low fluid level, the light can be coming on to indicate an internal hydraulic fault in the master cylinder or elsewhere in the hydraulic part of the brake system.

Besides any of the above, the parking brake light activates the brake light using a switch on the parking brake pedal.
If everything else checks out OK, then when the light is on (preferably while you're stopped) pry up on the parking brake pedal with your foot.
If the light goes out, then you know that the pedal is sitting too low, which could be a sticking cable or other mechanical parking brake part sticking.
Sometimes the ratcheting mechanism of the parking brake lever itself wears out.

Unless a car has wired brake pad sensors (most do not), and assuming the fluid level in the master cylinder is optimal, then worn brake pads will not turn on a brake warning light.
Problems with rotors do not turn on the brake warning light.

FWIW, the ABS light being on could just be a poor ground or poor connection but troubleshooting with an advanced scan tool is required if all the connections are all good and clean.

Hope this helps you out.

Thanks for the input. Sorry I should have been more specific about the gas cap thing. We have had the code read, and it is the gas cap. The DIC also says "CHECK GAS CAP". I guess we've never really gotten around to replacing it. We also did open the brake fluid reservoir, and it was full (almost to the brim, the confusing thing wad that there was no "fill to here" line).

I think I'll start with the parking brake troubleshoot like you mentioned. If that's not it, I'll go ahead and get the codes read to narrow it down. There are no leak spots on the garage floor, so if it is a leak, it is small. Or, like you said, it could be an internal hydraulic failure. We shall see.

Thanks again for the help!

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brownishSLE
"Family heirloom" Brown-on-brown 2000 SLE

It's not winter anymore.
I'll get a new photo up
soon.

You're welcome.
I'm surprised there were no min or max fill lines. Sometimes they're tough to see because they're only on 1 side of the reservoir and they're the same color as the rest od the reservoir, instead of being painted for better visibility.
Sounds like the master may be overfilled but that wouldn't cause a warning light.

If the fluid had been too low at one point, the sensor inside the master cylinder may have gotten stuck.
Some reasonably gentle taps on the aluminum body of the master cylinder may free it, so that it works again.

Hope you'll post back when you pinpoint the cause.