If it's a matter of a couple of bucks for the parts that's what a mechanic is going to charge you. The "$100's" you're assuming you're going to be charged is for labor and helps cover the thousands of dollars the shop spends every year on tools, equipment, continuing training, taxes, government regulations, insurances, and the mechanic's expertise and experience.
The problem is GM's silly daytime running light circuits are extremely complicated so while it is often a simple and inexpensive repair, the diagnostics and testing to get to that repair is not so simple. Based on your observation that the lights went out, then worked again for a little while tells you the bulbs are not the problem. It's very unlikely two would burn out at the same time, and even if they did, they wouldn't work again briefly later.
Instead of turning the low beams on automatically, which requires common sense that the engineers are lacking, they use an unreliable computer module to turn the high beams on and off hundreds of times per second resulting in them running at 80 percent of normal brightness and glaring into people's rear-view mirrors. That means you can't make any observations about the low beam filaments by looking at the daytime running light system.
The place to start is at the headlight switch. Look at the connector for signs it has melted or there's two terminals that are overheated and blackened. Also look on the switch to see if any terminals are black or loose. If no obvious problem is found, check the connector on the dimmer switch. If nothing is found there you will need the wiring diagram in the service manual and you'll need to take some voltage readings to find where the break is in the circuit. If you don't know how to interpret those voltage readings, THAT'S where the mechanic's expertise becomes a good value.
A less-desirable way to start the diagnostics is by substituting parts. Professionals never do this because it is the most costly and least effective way to diagnose a problem, but for you to get the process started yourself, you will find a lot of these cars in the salvage yard. If you have one of the "pick-your-own-parts" yards nearby, the parts are usually pretty inexpensive. You can try the switches, and you might get lucky. If one of them does get the lights working, again check the old switch and the connector for signs of overheated terminals. If there are two and they're not replaced they will cause a poor connection which results in heat, and that will eventually lead to a repeat failure. Mechanics are very aware of those repeat failures and they know how to prevent them. That's a perfect example of how a used switch can cost a couple of dollars and you think that's all that's needed to fix the car, but the mechanic knows the proper and permanent fix requires replacing the terminals or complete connector, and that takes time. Also remember you're working on your car for free. You wouldn't work on someone else's car for free.
Thursday, June 6th, 2013 AT 1:20 PM