A backfire is the loud pop or bang you hear from the exhaust (or sometimes from under the hood). It happens when unburned fuel ignites somewhere it shouldn't - usually in the exhaust system or intake manifold. The most common causes are an engine misfire, a timing problem, or an exhaust leak letting air in where the raw fuel can ignite.
Repeated backfires can melt your catalytic converter ($1,000-2,000 to replace), damage exhaust valves, and crack exhaust manifolds. If your check engine light is flashing, pull over - that's an active misfire causing the backfires. Get it diagnosed this week.
When a cylinder doesn't fire, raw fuel goes out into the hot exhaust where it ignites - bang. The most common root cause is old spark plugs or a failing ignition coil. Fix this fast or you'll cook your catalytic converter.
View Full Diagnosis - P0300 →A single cylinder dumping unburned fuel into the exhaust causes regular popping or backfires. The fix is usually a $25 spark plug or $60 coil on the offending cylinder. Easy to diagnose by swapping coils.
View Full Diagnosis - P0301 →A failing catalytic converter (often caused by a long-ignored misfire) restricts exhaust flow and contributes to backfiring. Often shows up alongside misfire codes.
View Full Diagnosis - P0420 →A cracked exhaust manifold or loose flange before the catalytic converter lets oxygen mix with unburned fuel - causing pops and bangs. Often produces no codes but is loud and noticeable. Fix is $50-300.
View Full Diagnosis - Diagnosis Guide →On older cars (pre-2000s) timing can drift out of spec and cause backfires. On newer cars, timing is computer-controlled but can be affected by a failing crank or cam sensor. Look for codes P0335, P0340.
View Full Diagnosis - P0335 →Describe your symptom (or paste your code) and our AI gives you the exact most-likely fix, parts list, and cost - in under 30 seconds. $5.99. One report, no subscription.
Get My Repair Report →Diagnose before backfires destroy your catalytic converter.
If your scan tool is showing one of these codes alongside this symptom, that's your starting point. Click any code for the full diagnosis, common causes, and repair costs.
A backfire happens when unburned fuel reaches the hot exhaust and ignites. The two most common causes are an engine misfire (a cylinder isn't firing, so raw fuel exits) or an exhaust leak (oxygen sneaks in and ignites unburned fuel before the catalytic converter).
Short trips to the shop, yes. But repeated backfires destroy catalytic converters fast - what could be a $50 spark plug fix can become a $1,500 catalytic converter replacement in a few hundred miles. If the check engine light is flashing, stop driving immediately.
Yes - this is the #1 cause. Worn plugs misfire under load, dumping raw fuel into the hot exhaust where it ignites with a bang. If you haven't replaced your plugs in 60,000+ miles, that's the first place to look. Plugs are $20-80 in parts.
Spark plugs: $20-80 in parts. Ignition coil: $30-90. Exhaust gasket: $20-60 plus labor. Cracked exhaust manifold: $200-600 with labor. Catalytic converter: $400-2,000. The damage from ignoring backfires usually costs more than the original fix.