Why cars catch fire while driving

Most in-motion car fires start when a mechanical or electrical fault ignites flammable fluids or materials near hot engine or exhaust components; crash damage and, in electric vehicles, battery failures are other major triggers. While the overall likelihood is low, modern vehicles carry abundant ignition sources, energy, and combustibles. Understanding how these fires begin, the warning signs, and what to do can dramatically improve safety and reduce risk.

How vehicle fires start: the fire triangle on wheels

Every vehicle carries all three elements of the fire triangle—fuel, heat, and oxygen. Gasoline or diesel, engine oil, transmission and power-steering fluid, brake fluid, and even interior plastics can serve as fuel. Heat comes from engines, exhausts, catalytic converters, brakes, and electrical shorts. Oxygen is plentiful in the air stream. When a leak, fault, or crash brings fuel and heat together, ignition can occur within seconds.

The items below outline the primary heat sources and fuels present in moving vehicles.

• Heat sources: hot exhaust parts (including catalytic converters and diesel particulate filters), engines and turbochargers, overheated brakes and tires, electrical shorts/arcing, and, in hybrids/EVs, high-voltage systems under fault.
• Fuels: gasoline/diesel, engine oil, transmission and steering fluid, brake fluid, windshield washer fluid (often methanol-based), interior and underhood plastics and insulation; most coolant mixtures are not easily ignited but can burn under the right conditions.

Taken together, these elements mean that a small leak, frayed wire, or damaged component can escalate quickly, especially at highway speeds where airflow feeds flames and spreads burning fluids.

Leading causes while driving

Although specifics vary by vehicle type and circumstance, investigators consistently find mechanical and electrical failures at the root of most highway vehicle fires, followed by crash-related fires. The sections below detail common patterns for internal-combustion and electrified vehicles.

Internal-combustion vehicles (gasoline and diesel)

Conventional cars and trucks rely on flammable liquids and hot exhaust systems, so heat + leak + spark is the typical recipe. These are the most frequent culprits seen by fire services and roadside investigators.

• Fuel or oil leaks onto hot parts: Perished hoses, loose clamps, cracked lines, or failed gaskets drip gasoline, diesel, or oil onto manifolds, catalytic converters, or turbos.
• Electrical shorts and aftermarket wiring: Chafed wires, corroded connectors, misrouted amp or light-bar cables, incorrect fuses, and unfused battery leads can overheat and ignite nearby plastic looms or sound insulation.
• Overheated catalytic converters/exhaust: Misfires dump raw fuel into the exhaust, superheating the catalyst; parking or driving over dry vegetation can ignite ground fires that spread to the vehicle.
• Brake or tire overheating: Stuck calipers or dragging parking brakes ignite pads or wheel-well liners; underinflated or overloaded tires overheat and can catch fire after a blowout.
• Transmission or power-steering failures: High pressure fluid sprays onto hot components after hose or seal failure.
• Diesel particulate filter (DPF) regeneration: Elevated exhaust temperatures during active regen can ignite nearby combustibles if faults or leaks are present.
• Collision damage: Ruptured fuel systems or severed wiring in a crash can ignite quickly, especially if airbags or pretensioners generate hot particles and there are spills.

Regular inspection of hoses, clamps, wiring, and exhaust components—and prompt repair of misfires or leaks—significantly reduces these risks.

Electric and hybrid vehicles

Electrified vehicles have far fewer flammable liquids but carry high-energy lithium-ion batteries and complex electrical systems. Their overall fire incidence appears comparable to or lower than gasoline vehicles, according to safety agencies, but battery fires behave differently and are harder to extinguish.

• Battery thermal runaway: Triggered by internal cell defects, external heat, crushing/penetration from debris or curbs, or overcharging due to hardware/software faults. Runaway can propagate through modules and may re-ignite hours or days later.
• High-voltage system damage after impact: Underbody strikes or collision forces can compromise the pack, coolant loops, or high-voltage connectors.
• 12‑volt wiring faults: Conventional low-voltage systems still power lights, infotainment, and add-ons; shorts and poor splices can ignite interiors just as in ICE cars.
• Charging equipment issues: Damaged cables/connectors, non-compliant adapters, or poor receptacles can overheat; most onboard systems will fault-safe, but not always.
• Saltwater immersion and corrosion: After flooding, conductive paths can form and cause delayed high-voltage faults and fires once the car dries.

EVs and hybrids incorporate extensive safety monitoring and contactors to isolate faults, but any significant underbody strike, pack alert, or charging anomaly warrants professional inspection before further driving.

Contributing risk factors

Some conditions magnify the chance that a small issue becomes a roadside fire. Being aware of these can help you intervene early or avoid them altogether.

• Poor or deferred maintenance: Aging hoses, seals, and wiring insulation fail more often; old cars and high-mileage work vehicles are overrepresented in fire statistics.
• Aftermarket modifications: Audio amplifiers, remote starters, light bars, and hardwired dashcams without proper fusing and routing commonly spark fires.
• Open recalls and technical service campaigns: Many fire-related defects are addressed by manufacturers—ignoring recall notices leaves known risks uncorrected.
• Carrying flammables: Gas cans, solvents, aerosol products, or lithium e-bikes/scooters in the cabin can accelerate or start fires, especially in hot weather.
• Overloading/towing: Excess weight overheats transmissions, engines, and brakes.
• Rodent damage: Chewed wiring and nests in the engine bay create ignition sources.
• Extreme heat and terrain: Heat waves, steep grades, and parking over dry grass increase temperatures and exposure to combustible materials.

Addressing these risk factors—particularly maintenance, recalls, and safe accessory wiring—prevents many in-motion fires before they start.

Warning signs while driving

Fires often announce themselves minutes before visible flames. Recognizing early symptoms lets you stop safely and prevent escalation.

• Burning smells: Sweet, acrid, or plastic odors; hot oil or electrical insulation smells from vents.
• Smoke or “steam” from the hood or wheel wells: White steam from coolant is different from gray/black smoke; any smoke is a red flag.
• Warning lights and gauges: Battery/charging, check engine (especially misfire), high coolant temperature, or brake warnings.
• Loss of power or rough running: Misfires can overheat the catalyst rapidly.
• Repeated fuse blows or flickering lights: Indicates an electrical short.
• Hot brakes or burning rubber smell: Possible dragging brake or tire issue.
• Visible drips or trails: Oily or fuel odors after a bump or scrape suggest a leak.

If you sense any of these, treat it as urgent: pull over safely, shut down, and investigate from a distance rather than “limping home.”

What to do if you suspect a fire

Your priority is getting people out and away, then alerting responders. These steps reflect common guidance from fire services and highway safety agencies.

1. Signal, move to the shoulder or a safe turnout, stop, shift to Park/Neutral, set the parking brake, and turn off the engine or traction system.
2. Evacuate everyone immediately; move upwind at least 100 feet (30 meters) and behind a barrier if possible.
3. Call emergency services and state your location, vehicle type (gasoline, diesel, hybrid, or EV), and whether smoke or flames are visible.
4. Do not open the hood or trunk; introducing air can flash the fire. Keep doors closed once everyone is out.
5. Use a fire extinguisher only if the fire is very small, you are trained, and you have a suitable unit (ABC for most cars; some departments recommend additional Class D capability for certain battery fires). Aim at the base and retreat if it doesn’t go out immediately.
6. For EVs/hybrids, alert responders to high-voltage risks; keep clear of the underbody and wheels. After a crash or underbody strike, treat the vehicle as energized even if there is no smoke.
7. In tunnels or parking structures, follow posted emergency procedures, use emergency bays, and evacuate promptly.

Vehicles can reignite, especially EVs and hybrids after battery damage, so do not re-enter the car until cleared by responders.

Prevention and maintenance tips

Most vehicle fires are preventable with routine care and a few simple habits. The points below focus on defects and behaviors commonly implicated in fire investigations.

• Fix leaks fast: Any fuel, oil, coolant, or washer-fluid leak should be addressed immediately; clean oil-soaked engine bays after repairs.
• Stay current on service: Replace cracked belts and hoses; repair misfires promptly to protect the catalytic converter.
• Check recalls: Run your VIN at your national safety agency’s recall site (e.g., NHTSA in the U.S.) and complete repairs without delay.
• Wire accessories correctly: Use the right gauge, add fuses within 15–30 cm of the battery feed, protect cables with grommets, and avoid “add-a-circuit” overloads.
• Use correct fuses: Never upsize a fuse to stop it blowing; find and fix the underlying fault.
• Mind the exhaust and underbody: Don’t park over dry grass; after road-debris strikes or off-roading, inspect for fluid leaks and damaged shields.
• Brake and tire care: Maintain pressures, replace worn pads/rotors, and investigate pulling or drag immediately.
• EV/hybrid specifics: Use manufacturer-approved charging equipment, replace damaged charge cables, install software updates, and seek inspection after curb or debris impacts or after saltwater flooding.
• Store flammables safely: Keep gas cans, solvents, and lithium e-bikes/scooters out of hot vehicles; never in the passenger cabin.
• Carry a suitable extinguisher: A compact, accessible ABC extinguisher can stop a small fire from growing.

These steps reduce both the probability of a fire and the severity if one starts, buying you crucial time to exit and call for help.

After a vehicle fire

Once everyone is safe and responders have cleared the scene, contact your insurer and, if relevant, the vehicle manufacturer. Preserve photos and details for investigators, and report potential defects to your national safety authority (such as NHTSA in the U.S.). Do not attempt to restart or recharge a fire-involved vehicle; have it towed to a secure facility. For EVs and hybrids, be aware of re-ignition risk and follow responder and manufacturer guidance for quarantine and monitoring.

The bottom line

Cars catch fire while driving when heat sources—engines, exhausts, or electrical faults—meet flammable fuels or materials, often due to leaks, wiring issues, or crash damage. Most incidents are preventable with maintenance, proper accessory installation, prompt attention to warning signs, and safe responses if trouble starts. Knowing the risks—and how to act—keeps small problems from becoming dangerous roadside fires.

Summary: In-motion vehicle fires are typically caused by mechanical or electrical failures that ignite fluids or plastics; crashes and, in EVs, battery damage are additional triggers. Watch for smells, smoke, and warnings; pull over and evacuate if suspected; and reduce risk through maintenance, recall completion, careful wiring, and safe charging practices.