* Low Brake Fluid: The most likely culprit. During the head gasket repair, there's a chance brake fluid was accidentally spilled or disturbed. Even a small leak can cause a significant drop in fluid level, leading to a hard pedal and the brake light illuminating. Check your brake fluid reservoir immediately. If it's low, this is your problem. You'll need to add fluid and *then* find the leak. Adding fluid is a temporary fix; you must locate and repair the leak.
* Air in the Brake Lines: If the brake system was disturbed (unlikely during a head gasket repair, but possible if other work near the brake lines was done), air might have entered the lines. This causes a spongy or hard pedal and can trigger the brake light. Bleeding the brakes would be necessary.
* Master Cylinder Issues (Rare, but possible): While unlikely directly related to the head gasket job, the process *might* have somehow vibrated or damaged the master cylinder. A failing master cylinder can also lead to a hard pedal and brake light.
* Brake Booster Vacuum Leak (Unlikely): The brake booster uses engine vacuum. While extremely unlikely, significant vacuum leaks *could* be created or exacerbated by improper head gasket repair if vacuum lines were near the work area. However, you'd likely notice other engine issues first, like rough running.
What to do:
1. Check the brake fluid reservoir immediately. If it's low, add DOT 3 brake fluid (the correct type for your car). Do *not* drive the car until you've determined the source of the leak.
2. If the fluid is low, carefully inspect the brake lines, calipers, and wheel cylinders for any signs of leaks. Look for wetness, dripping fluid, or puddles under the car.
3. If you're comfortable, bleed the brakes. If not, take it to a mechanic. Bleeding removes air from the brake lines.
4. If the fluid level is normal and the brakes are still hard, it's time for a professional inspection. The problem is likely more serious and requires a mechanic to diagnose the issue.
Do not drive the car with a hard brake pedal and illuminated brake light. This is a serious safety hazard. Get it checked immediately. The head gasket repair is irrelevant unless brake components were damaged during the work, which is unlikely. Focus on the brake system itself.
