In many Pontiac G6 models, the third brake light (the center high-mounted stop lamp, or CHMSL) stops working primarily due to a blown bulb, a blown fuse, or a faulty brake light switch. Start with these basics to diagnose the issue and avoid unnecessary repairs.
On the G6, the CHMSL sits at the rear of the vehicle and can use either an incandescent bulb in the housing or an LED module, depending on the year and trim. If the other rear brake lights work but the CHMSL remains dark, the problem is often isolated to the CHMSL bulb/LED, its housing connector, or associated wiring rather than the main brake-light circuit. More complex failures—such as a faulty brake light switch, a damaged wiring harness, or a problem in the vehicle’s body control module—are less common but possible.
Common causes of a non-working CHMSL
These are the most frequent culprits when the third brake light isn’t functioning on a Pontiac G6.
- Blown CHMSL bulb (incandescent) or failed LED module within the CHMSL assembly
- Blown fuse for the stop lamp/CHMSL circuit
- Faulty brake light switch at the brake pedal
- Water intrusion or moisture in the CHMSL housing causing corrosion or shorting
- BCM (body control module) or related wiring harness fault
Note: If your G6 uses an LED-based CHMSL, an LED module failure often requires replacing the entire CHMSL assembly rather than a simple bulb change.
If you’ve checked these common causes and the CHMSL still won’t light, you may be dealing with a more complex electrical fault or a recall/service bulletin issue that requires professional service.
Diagnosis and DIY fixes
Before you start, remember to observe safety precautions when working on electrical components. If possible, disconnect the battery before removing any interior or exterior trim to access the CHMSL.
- Verify whether the other rear brake lights illuminate when you press the brake pedal. If all rear stop lights are affected, the issue is more likely the brake light switch, fuse, or BCM; if only the CHMSL is out, focus on the CHMSL itself and its wiring.
- Inspect and replace the CHMSL bulb (for incandescent CHMSL) or the LED module (for LED CHMSL). For incandescent bulbs, you may access the CHMSL housing from the trunk; replace with the correct bulb type. For LED units, replacement often means swapping the entire CHMSL assembly.
- Check the fuse(s) labeled for Stop Lamps or CHMSL in your interior and/or under-hood fuse box. Replace blown fuse with the correct rating as specified in the owner's manual.
- Inspect the brake light switch at the brake pedal. A faulty switch can cause one or more brake lights to fail or stay off. If the switch is out of adjustment or defective, replace or adjust it according to the service manual.
- Examine wiring and connectors at the CHMSL housing and along the tail-light circuit for damaged insulation, pin corrosion, or loose connectors. Reseat any loose connectors and clean corrosion if present.
- Test for voltage at the CHMSL connector when you press the brake pedal. Use a multimeter or a test light. If you see voltage but the light doesn’t illuminate, the bulb/LED module or the housing is defective and should be replaced. If there’s no voltage, the fault lies upstream (switch, fuse, or wiring).
- If the CHMSL is LED and cannot be repaired, consider replacing the entire CHMSL assembly. In some cases, a dealer or professional shop can diagnose deeper issues (such as BCM communication) that are not user-serviceable.
Most straightforward CHMSL problems are resolved with a bulb or fuse replacement, or a simple switch adjustment. If the diagnose-and-replace steps don’t restore function, professional diagnostics are recommended to check for BCM or wiring harness faults.
Recall and service bulletin notes
CHMSL-related issues can sometimes be part of recalls or service bulletins. Check your Vehicle Identification Number (VIN) against NHTSA’s SaferCar.gov database and GM’s service bulletin listings to see if your G6 is affected and eligible for a free repair or replacement.
Summary
The most common reasons the Pontiac G6’s third brake light fails are a blown bulb or LED module, a blown fuse, or a faulty brake light switch. Start with these basics, then inspect wiring and connectors, and test for proper voltage. If simple fixes don’t restore function, consider LED-module replacement, BCM-related diagnosis, or professional service. Regularly check for recalls or service bulletins using your VIN to ensure you’re addressing any manufacturer-reported issues.