If your windshield fogs up frequently, it can seriously reduce visibility and create unsafe driving conditions. Fogging happens when moisture condenses on the glass due to temperature and humidity differences between the inside and outside of the car. While occasional fogging is normal, persistent issues can point to problems with your vehicle’s ventilation or heating system.

What does it mean if your windshield fogs up?

It usually means that excess moisture is trapped inside your vehicle or that the defogging/defrosting system is not working properly. This can prevent the windshield from clearing quickly, making it harder to see the road.

Common causes of windshield fogging

• Faulty or weak defroster system
• Blocked or dirty cabin air filter
• Malfunctioning air conditioning or heater controls
• Coolant leak into the cabin (heater core issue)
• Excess moisture from wet carpets, leaks, or weather

Why do you need to fix this problem quickly?

Poor visibility is a major safety hazard. If fogging is caused by a coolant leak or heater core problem, it can also allow toxic fumes into the cabin and cause further vehicle damage. Fixing the issue ensures safe driving and prevents costly repairs.

How do you know when to get it checked?

You should book an inspection if:

• Your windshield fogs up regularly and does not clear easily
• The defroster takes unusually long to clear fog
• You notice a sweet smell inside the cabin (possible coolant leak)
• Other windows fog up excessively while driving

What happens during an assessment?

A mechanic will:

1. Check the operation of the heater, air conditioning, and defroster systems
2. Inspect and replace the cabin air filter if blocked
3. Look for coolant leaks from the heater core
4. Test for water leaks into the cabin from seals or drains
5. Ensure proper airflow through the ventilation system

How much does it cost to fix?

Costs depend on the cause. Cabin air filter replacement typically costs $80–$150. HVAC or control repairs range from $200–$600. Heater core replacement can cost $800–$1,500+ due to labour intensity.

Is it unsafe to drive with a fogging windshield?

Yes. Driving with a fogged-up windshield significantly reduces visibility and increases the risk of accidents. If your defogger system isn’t clearing the glass properly, it should be inspected and repaired immediately.