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How to Fix Chevrolet Cobalt Brake Light Fail
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When it comes to automotive safety, brake lights play a crucial role. They signal to other drivers that you are slowing down or stopping, thus preventing rear-end collisions. If you're driving a Chevrolet Cobalt and facing an issue where only the third brake light turns on while braking, this guide is for you. Combining insights from several troubleshooting threads, we'll walk you through the steps to diagnose and fix this common problem.
Understanding the Problem
In the Chevrolet Cobalt, the brake light system comprises the high brake light and brake bulbs on either side. The brake switch provides a ground to these lights and deactivates cruise control if engaged. The high brake light receives battery B+ power, different from the tail brake light, which gets ignition 1 B+. The brake lamp fuse is responsible for the tail brake lights, not the high brake lights. The rear tail brake lights work only when the ignition is on (with a good fuse), whereas the high brake lights come on as soon as you touch the brake pedal.
Chevrolet Cobalt Brake Light Fail - Troubleshooting Steps
Check the Fuses
Start by checking the brake fuse. A common misconception is that if the high brake lights work, the fuse must be fine. This isn't always the case. Check fuse #9 (10 amp) on the BCM fuse block located in the passenger side center console.
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Inspect the Bulbs and Sockets
Although the bulbs might seem fine, it's worth double-checking them and their sockets for any damage or poor connections.
If your brake light bulb is burned out, it needs to be replaced. To find out which bulb you need for your Chevy Cobalt, check the chart below:
Test the Wires
Use a multimeter to test the wires going to the brake lights. You should look for ground when the brakes are applied. If there's no current, there could be an issue with the wiring or connectors.
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Examine the Body Control Module (BCM)
The BCM controls the stop lamps. When you press the brake pedal, the BCM receives a signal from the brake pedal position sensor and supplies voltage to the stop lamp assemblies. The stop lamps are grounded at G401 and G403, and the CHMSL is grounded at G302.
If the 4-way flashers work at the back, but the brake lights don't brighten up when braking, this points towards a BCM issue. Check pins "A9 and A12" of C3 of the BCM to see if you have voltage when applying the brake with the ignition on.
Brake Light Switch/Sensor
The brake light switch (or sensor) might need a relearn procedure with a scan tool after replacement. If the BCM detects a problem, it will set a code, and the stop lamps might always be on when the vehicle is running.
Professional Assistance
If the above steps don't resolve the issue, it might be time to seek professional help. A garage with a Tech 2 scanner can be invaluable in diagnosing complex BCM or wiring issues.
Conclusion
Repairing the brake lights on a Chevrolet Cobalt involves a systematic approach to diagnosing and addressing electrical issues. Starting with simple checks like fuses and bulbs, and moving onto more complex components like the BCM, you can often identify and fix the problem without needing expensive dealership services. However, if you're not comfortable working with vehicle electrical systems, it's always best to consult a professional. Remember, safety is paramount, and functional brake lights are non-negotiable on any vehicle.
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Nick Marchenko, PhD
Industrial Engineer & Automotive Content Specialist
Nick writes in-depth guides on car clubs, engine specs, vehicle ownership, and modifications, combining engineering knowledge with automotive passion.
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