Gas Mileage Dropped? What Your Car’s Telling You

Filling up way more often than usual? If your car’s drinking like a sailor on shore leave, something’s wrong.

Why It Happens

Engines are designed to run at a sweet spot of air, fuel, and spark. When that balance tips, the ECU compensates by dumping more fuel. Could be sensors lying, injectors leaking, or tires dragging. Sometimes it’s simple — like underinflated tires. Other times it’s a failing O2 sensor quietly killing your MPG.

Most Common Causes

• Low tire pressure – kills economy faster than you think.
• Clogged air filter – chokes airflow, engine burns more fuel.
• Faulty oxygen sensor – ECU dumps fuel, cat suffers.
• Dirty fuel injectors – poor spray pattern wastes fuel.
• Dragging brakes – caliper stuck, car fights itself.
• Short trips/cold weather – engine never warms up, efficiency tanks.

What You Can Check

What a Mechanic Will Check

• Scan ECU for sensor faults (O2, MAF, fuel trims).
• Test fuel injectors for spray and leaks.
• Inspect brakes and wheel bearings for drag.
• Run compression or leak-down tests if internal wear suspected.

Ballpark Repair Costs

• Tire inflation/rotation: Free–$50.
• New air filter: $30–$70.
• O2 sensor replacement: $150–$300.
• Injector service/replacement: $150–$400 each.
• Brake caliper replacement: $250–$500 each.

When to Call It Quits

A couple MPG lost in winter? Normal. But if you’re suddenly down 20–30%, don’t shrug it off. Burning excess fuel hurts your wallet, clogs your cat, and can toast the engine over time.