"How much does it cost to fix a misfire?" has no single answer, because a misfire is a symptom — codes P0300 and P0301–P0308 can be caused by anything from an $8 spark plug to a blown head gasket. This page gives realistic 2026 US parts-and-labor ranges by root cause, so you can size the repair once you know what's actually wrong. To find the cause first, start with our misfire diagnosis guide.
How we estimate these costs
Ranges below assume a US independent shop at a labor rate of roughly $110–$160 per hour (dealers run higher; rural shops lower), plus typical aftermarket-to-OEM parts pricing for a mainstream 4-, 6-, or 8-cylinder vehicle. Exotic, European, and hard-to-reach engines cost more. "DIY parts" is the parts-only cost if you do the work yourself. These are planning figures, not a quote — always get a written estimate for your specific vehicle.
Misfire repair cost by cause
Root cause
Shop (parts + labor)
DIY parts only
Spark plugs (full set)
$120–$400
$25–$120
Ignition coil (single)
$150–$350
$40–$180
Ignition coils (full set/pack)
$400–$850
$150–$500
Fuel injector (one)
$300–$700
$60–$300
Vacuum / intake leak repair
$150–$500
$20–$150
EGR valve
$250–$600
$80–$300
Compression / leak-down diagnosis
$150–$300
tool: $40–$120
Head gasket
$1,500–$4,000+
$60–$250 (gasket set)
Catalytic converter (misfire damage)
$1,000–$3,000
$200–$1,200
Diagnosis + minor fix
$100–$300
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Where the DIY savings are real (and where they aren't)
Worth doing yourself: spark plugs and a single accessible coil are the highest-value DIY jobs — the parts are cheap and most of the shop bill is labor. On many 4-cylinder engines you can do plugs and a coil in under an hour with basic tools.
Think twice: rear-bank coils on a transverse V6, fuel injectors that require intake removal, and anything involving compression loss (head gasket, valves) are labor-intensive and unforgiving. Here the shop's diagnostic certainty and warranty are usually worth the price.
Why diagnosis first saves money
The most expensive misfire repair is the wrong one. Replacing all the coils and plugs on a P0301 that was actually a leaking injector, or a burnt valve, means paying twice. A focused diagnosis — swap-testing the suspect cylinder and confirming spark, fuel, and compression — usually costs $100–$300 and tells you exactly which row of the table above applies. Follow the ordered steps in the diagnosis guide before you buy parts.
FAQ
Is it cheaper to fix a misfire yourself?
For plugs and an accessible coil, yes — you often save 50–75% because those bills are mostly labor. For injectors, head gaskets, or anything needing diagnosis equipment, the shop's certainty is usually worth it.
How much is a P0300 code to fix?
P0300 is a random misfire, so cost depends on the cause: a tune-up of plugs and coils runs $200–$850 at a shop, a vacuum leak $150–$500, and a mechanical fault (head gasket, valves) $1,500 and up. Diagnose before you buy.
Why did my misfire ruin my catalytic converter?
An active misfire dumps unburned fuel into the exhaust, which ignites in the converter and melts its internal honeycomb. That's why a flashing check engine light is urgent — ignoring it can turn a $200 coil job into a $1,000–$3,000 converter job.
Costs are 2026 US ballpark ranges for planning only, not a quote, and not a substitute for a written estimate from a licensed shop. Prices vary widely by region, vehicle, and parts choice.