P0301 Fixes Cost $100 to $1,020. Swap the Coil First

A P0300 tells you the engine is missing somewhere. A P0301 tells you exactly where, and that one digit makes this code much cheaper to chase. The computer has already done half the work by naming cylinder 1. What it can't tell you is whether the plug, the coil, the injector or the engine itself let that cylinder down.

I'm Anthony, lead technician at Supercanic, the shop in San Jacinto and Hemet that runs MechanicRank, where we list 48,078 shops and mechanics. On a single cylinder misfire, the first test costs nothing. You move the coil to another cylinder and see if the code moves with it. That one step decides whether you spend $100 or $1,000.

What P0301 Means

California's OBD II rule, 13 CCR 1968.2, says the engine computer has to identify the specific cylinder that is misfiring. When more than one cylinder misses, it sets a separate multiple cylinder code instead. That's the P0300.

So the last digit is the cylinder number. P0301 is cylinder 1, P0302 is cylinder 2, and so on up to the engine's last cylinder. The same rule defines a misfire as a cylinder that fails to burn because of no spark, poor fuel metering or poor compression. Those three are your whole suspect list.

Where cylinder 1 sits changes from engine to engine. Don't guess. The repair manual for your engine, or the firing order diagram a parts counter can print, shows which one it is. Pulling the wrong coil is how a free test turns into a wasted afternoon.

What Each Usual Fix Costs

These are typical independent shop prices from our own repair cost guides. Each one adds the part price to the book labor time at $95 to $140 an hour. The California column uses $120 to $175 an hour. The diagnostic row is what independent shops post on their own websites.

MechanicRank repair cost guides as of October 2026. A midsize sedan or small SUV. Trucks, hybrids and European cars cost more. Posted diagnostic fees are the middle half from 504 independent shop websites. Before sales tax. Not a quote for your car.

The top three rows cover most single cylinder misfires on a car that's been maintained. The bottom two are what you pay when the cause is air or the engine itself. That's why the order of testing matters more than the price of any one part.

A real job shows how this plays out. We had a 2006 Dodge Grand Caravan on October 8, 2026, booked as a diagnostic. The scan showed P0300, P0303 and P0306, so two single cylinder codes plus the general one. Testing found the spark plugs fouling out. The bill was $150 for the diagnosis, three plugs at $8 each and one hour of labor at $125. That came to $299, on a van whose code list looked like a coil job or worse.

The Free Test That Settles Most of It

A single cylinder code lets you do something a P0300 never does. You can move a part and watch the code follow it.

• Save the data first. Write down the freeze frame and the misfire counts before anyone clears a code. That's the best clue you have.
• Swap the coil. Move the cylinder 1 coil to cylinder 2 and put that coil on cylinder 1. Drive it the same way it was driven when the light came on.
• Read the result. If the code comes back as P0302, the coil is bad. Buy one coil, not a set.
• Swap or pull the plug next. If the code stays P0301, pull the cylinder 1 plug. Look for oil, black soot, a cracked tip or a worn gap.
• Check fuel and air. If plug and coil both check out, the shop tests the injector and looks for a vacuum leak at that cylinder's intake runner.
• Test compression last. A compression or leakdown test on cylinder 1 tells you whether the engine itself is the problem.

Our repair guide for ignition coils calls the swap one of the most useful tricks in a driveway, because it costs nothing. On a four cylinder with coils on top, it takes minutes. On a V6 with the coil on the back bank under the intake, it can mean pulling the intake first. That's where the labor hours in the table come from, and it's a fair reason a shop charges for diagnosis.

Our free lesson on misfires shows how a tech reads the misfire counts on a scan tool.

What Our Own Jobs Show

We keep a public study of what Supercanic customers actually paid. It covers 953 paid jobs from August 2025 to October 2026, and 92% were done at the customer's home or work. The full table is on our mobile mechanic prices page.

Supercanic paid jobs, August 2025 to October 2026, before sales tax. Most were in Riverside and San Bernardino counties. Middle half is the 25th to 75th percentile.

About one job in four was a diagnostic and nothing else. Finding the problem is often the whole job. The plug and coil jobs landed at a $214 median, close to the low end of our California guide range.

The fuel jobs cost more than twice that. So if a shop wants to start a P0301 with an injector, ask what test proved it. A coil swap and a plug pull should both come first, then a test of the injector itself.

Why a New Plug Can Foul Again

NGK, the spark plug maker, calls fouling the most common type of spark plug problem. Fuel, oil or carbon coats the tip, and the spark leaks down the coating instead of jumping the gap. The cylinder misses. NGK adds that a plug has to reach about 450 C to burn itself clean, and that short trips and slow driving keep it below that.

NGK also warns that a new plug may only fix a fouling problem for a while. If whatever fouled the old plug is still there, the new one fouls too. On a P0301, the usual reasons are worth checking while the plug is out.

Oil in the plug well is the big one. Our valve cover gasket guide notes that oil pooling in the plug wells causes misfires and kills coils. A leaking tube seal can drown cylinder 1's coil and plug, and a new plug won't survive it. A wet, oily plug tip is a different story. A Chrysler 3.3 engine guide lists oil burning from worn rings or valve seals as one cause of a misfiring cylinder. That's a compression and oil use question, not a parts store question.

Flashing or Steady Changes Everything

Unburned fuel from cylinder 1 goes straight into the exhaust and burns inside the catalytic converter. That's how a $100 coil turns into a converter job.

The flashing light is written into the rule. Carmakers have to set a misfire level that would damage the converter, judged in 200 revolution windows. Once the car crosses it, the light has to blink once per second while the misfire is happening. A smaller misfire, judged over 1,000 revolutions, only turns the light on steady.

There's a catch. The same rule lets a car that shuts off fuel to the dead cylinder keep the light steady instead of blinking. So a steady light on an engine that shakes hard isn't proof the misfire is mild. If it's bucking, park it and call a mobile mechanic or a tow.

Old Advice That Stuck

Replace all the coils while you're in there. One bad coil doesn't mean four. On a four cylinder with coils on top, buy the one that failed the swap test. The exception is a V6 rear bank, where our coil guide says doing all three while the intake is off saves paying that labor twice.

It's only one cylinder, so keep driving. A steady light and a smooth idle can wait a few days. A shake, a blinking light or a fuel smell can't. One dead cylinder still sends raw fuel to the converter.

Clear it and see if it comes back. Clearing erases the freeze frame and the misfire counts. Let the shop read the stored data first, then clear it after the swap test so you can see where the code lands.

Before You Approve the Job

Run this list with whoever quotes you.

• Did the code move? Ask whether they swapped the coil and what happened. That one answer rules a part in or out.
• What did the plug look like? Oily, sooty or cracked each point to a different fix. Ask to see it.
• One coil or a set? Ask why if the quote covers more than the failed one.
• Is the converter OK? If the light was blinking, ask whether they checked it.
• Written estimate. The FTC says it should name the condition, the parts and the expected labor. It also says to ask for the replaced parts and whether the diagnostic fee applies if you go elsewhere.
• California drivers. The Bureau of Automotive Repair says the shop needs your OK before it starts and again before any added repairs. If parts come off to find the problem, there may be a teardown charge even if you say no.

Find a Shop for the Job

MechanicRank lists 48,078 repair shops and mechanics in 6,653 cities. Every listing shows the shop's phone, reviews and hours, and the phone rings the shop direct. Search your ZIP code and ask for a diagnostic before parts. If the scan shows misses on more than one cylinder, our P0300 random misfire page covers that code.

At Supercanic, our own shop, labor is $150 an hour, with a 90 day or 5,000 mile labor warranty.

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