Yes. A misfire means one cylinder isn't burning its fuel, and that raw fuel burns in the catalytic converter instead. A converter runs $2,280 to $2,480 at a shop (RepairPal). The part that usually causes the misfire, a coil or a set of plugs, runs $238 to $399.
If the check engine light is flashing, pull over and arrange a tow. If it's solid and the engine only stumbles now and then, drive straight to a parts store for a free code read and book a shop this week.
What a misfire actually is
A misfire is a cylinder that fails to fire on its stroke. The engine computer sees the crankshaft slow for a fraction of a turn, counts it, and sets a code once the count passes a threshold.
The codes are easy to read. P0301 is cylinder 1, P0302 is cylinder 2, and so on. P0300 is "random or multiple cylinder misfire," which means the computer saw misfires on more than one cylinder or couldn't pin them to one. RepairPal lists P0300 as an "urgent" code, in the group that can cause "severe damage to the vehicle."
You'll feel it as a shake at idle, hesitation when you press the gas, and a drop in power. On a four-cylinder, one dead cylinder is a quarter of the engine gone (YourMechanic). Fuel economy drops because the fuel going into that cylinder is wasted.
Why it's worse than it feels
The engine will usually keep running, which is the trap. The damage happens downstream.
A misfiring cylinder pushes a charge of unburned gasoline and oxygen out the exhaust valve. The catalytic converter sits a foot or two down the pipe, already hot, and that charge lights off inside it. Identifix, the shop diagnostic database, says an active misfire "can damage the catalytic converter" and will often set a P0420 code later. Edmunds goes further: a misfire can overheat the emissions system and, in a bad case, start a fire.
A flashing check engine light is the computer telling you this is happening right now. Edmunds' advice is to shut the car down and have it towed. Identifix says the same, and so does O'Reilly, which rates P0300 as "not recommended to drive."
The second problem is a mechanical one. YourMechanic's point is that a car that loses a second cylinder mid-merge can lose enough power to be a hazard in traffic.
Most likely causes, in order
Ignition parts first, then fuel delivery, then air leaks, then the expensive stuff. That's the order both O'Reilly and Identifix use, and it matches what shops find.
Cause | Typical code pattern | Shop cost (RepairPal) |
|---|---|---|
Worn spark plugs | P0300 or one cylinder, worse under load | $288–$399 for a set |
Failed ignition coil | Single cylinder code, P0301 to P0308 | $238–$320 per coil |
Clogged or dead fuel injector | Single cylinder, often with a fuel smell | $768–$953 |
Vacuum leak or intake gasket | P0300 plus lean codes, rough idle | Varies by what's leaking |
Bad fuel, weak fuel pump, clogged filter | P0300, worse at highway speed | Varies |
Low compression, valve or head gasket | Steady misfire that parts don't fix | Hundreds to thousands |
RepairPal's figures are national averages for parts and labor and don't include tax. A Toyota Camry plug job is $151 to $223 on the same site, while an F-150 is $299 to $391, so your engine's cylinder count and how buried the plugs are move the number a lot.
One warning from RepairPal that saves money: plugs, wires and coils produce the same symptoms, so test before you buy. The cheap move with a single-cylinder code is to swap that coil with a neighbor and see if the code follows it. If P0302 becomes P0304 after the swap, the coil is bad. If it stays on cylinder 2, look at the plug, the injector or compression.
Identifix also lists a weak battery and outdated engine computer software as causes. Both sound unlikely but come up on newer cars, and a dealer software update is cheaper than parts.
Can you keep driving, and for how long
Flashing light: no. Not to the shop, not home. The tow is cheaper than a converter.
Solid light with an occasional stumble: a day or two, gently, to get the code read and reach a shop. Keep revs low, avoid towing or hard acceleration, and don't let it idle for long periods. Every minute of misfire is more fuel in the converter.
The misfire that only shows up cold or in the rain and clears in a minute is the least urgent kind. It's still worth a code read, because it tends to turn into a steady misfire once a coil or plug finishes failing. That timeline is weeks, not months, in most cases.
A misfire that gets worse the longer you drive is the most urgent kind. Once the converter is partly melted it restricts exhaust flow, the engine loses more power, and the misfire gets worse. Identifix lists a restricted converter as a cause of P0300 as well as a result of it.
What it costs
Reading the code is free at AutoZone, O'Reilly and Advance. A shop diagnosis is $122 to $179 at an independent (RepairPal's Ford Explorer estimate), and most shops credit it toward the repair.
The best case is a $238 to $320 coil or a $288 to $399 set of plugs. The worst common case is an injector at $768 to $953 (all RepairPal). If you waited and the converter is gone too, add $2,280 to $2,480, or $1,511 average in CarMD's 2026 data as quoted by Edmunds.
Don't replace the converter first. Identifix is clear on this: fix the misfire, then replace the converter if it still fails. A new converter behind an untreated misfire dies the same way.
What to do today
- Look at the check engine light. Flashing means stop, switch off, and call a tow.
- Solid light: drive gently to a parts store and get the codes read for free. Photograph the printout.
- If the code is a single cylinder (P0301 to P0308), swap that cylinder's coil with the next one and see if the code moves. Many coils come off with one bolt.
- Check the obvious: a cracked plug boot, a loose coil connector, a vacuum hose that's fallen off.
- Book a shop with the code in hand. Budget $240 to $400 for a coil or plugs, and ask them to check the converter if the light was flashing for any length of time.
Sources
- RepairPal: P0300 Random/Multiple Cylinder Misfire Detected
- RepairPal: Ignition Coil Replacement Cost
- RepairPal: Spark Plug Replacement Cost
- RepairPal: Fuel Injector Replacement Cost
- RepairPal: Check Engine Light Diagnosis Cost, Ford Explorer
- RepairPal: Catalytic Converter Replacement Cost
- YourMechanic: Is It Safe to Drive With a Misfiring Cylinder?
- O'Reilly Auto Parts: Check Engine Light Code P0300
- Identifix: P0300 Code, the Guide to Diagnostics and Repair
- Edmunds: What Your Check Engine Light Is Telling You
Featured image: Spark plug by Razor512, CC BY 2.0. Source
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