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P0305: Cylinder 5 Misfire Detected

Severe

Quick answer

P0305 means the engine computer counted too many misfires on cylinder 5: the mixture in that cylinder is not burning when it should. The usual causes are a worn spark plug or a failing ignition coil on that cylinder, then an injector or a compression problem. A flashing check engine light means stop driving; raw fuel is overheating the catalytic converter.

What it means

The computer detects misfires by watching the crankshaft sensor. Each cylinder’s power stroke should push the crank a little faster; when cylinder 5 fires weakly or not at all, the crank slows for that fraction of a turn and the computer counts a miss. Enough misses in a set number of revolutions and it stores P0305, turns on the light, and on many vehicles cuts fuel to that cylinder to protect the catalytic converter. The 5 is the cylinder’s number in the manufacturer’s numbering, not its position in the firing order.

That number is the first thing to pin down, because cylinder 5 lives in a different place on every engine family. On a straight-six it is the second cylinder from the firewall. On most V6 engines it sits on the odd-numbered bank, and on transverse V6s that is often the rear bank against the firewall, the hard one to reach. On a GM small-block V8 it is the third cylinder back on the driver’s side; on a Ford modular V8 it is the front cylinder on the driver’s side, because Ford numbers 1 to 4 down the passenger bank and 5 to 8 down the driver bank. Your owner’s manual, a service diagram, or our vehicle pages will show the layout for your exact engine.

Once you know where cylinder 5 is, a single-cylinder misfire is one of the most satisfying codes to diagnose, because the free swap test settles it most of the time. Move cylinder 5’s coil to a neighbor and clear the codes: if the misfire follows the coil, buy a coil. If it stays on cylinder 5, look at the plug, then the injector, then compression. The pattern of when it misfires, cold, hot, at idle or under load, narrows it further before you touch a tool.

P0305 symptoms: what you'll notice

  • A steady, rhythmic shake or stumble at idle, like the engine has a limp, that smooths out as rpm rises or gets worse under load depending on the cause.
  • Hesitation, jerking or a flat spot when you accelerate, sometimes with a popping sound in the exhaust.
  • A flashing check engine light while driving: the computer is telling you unburned fuel is overheating the catalytic converter. Ease off and stop as soon as it is safe.
  • A drop in power and fuel economy, and a raw fuel smell from the tailpipe at idle.
  • Companion codes: P0300 (random or multiple misfire) when the cause is shared across cylinders, or lean, EVAP or cam-timing codes that point at a cause beyond cylinder 5 itself.

Common causes

Ordered from most to least likely.

  1. 1.

    Worn, fouled or cracked spark plug in cylinder 5

    The most common cause. A gap worn wide, oil or carbon on the tip, or a hairline crack in the porcelain lets the spark fail under compression pressure. Read the plug: it tells you what is happening in that cylinder.

  2. 2.

    Failing ignition coil (or coil boot) on cylinder 5

    Coil-on-plug coils crack, arc through the boot, or fail only when hot. The swap test proves it for free, and on some engines the coil boot alone is the fault.

  3. 3.

    Clogged, sticking or leaking fuel injector on cylinder 5

    A restricted injector starves the cylinder and misfires under load; a leaking one floods it and misfires at idle or on a hot restart. Injectors can be swap-tested like coils on many engines.

  4. 4.

    Vacuum leak or intake gasket leak at cylinder 5’s runner

    A leak that leans out just that cylinder: a cracked intake gasket, a split hose that feeds that runner, or a warped plastic manifold. Suspect it when the misfire is worst at idle and disappears under load.

  5. 5.

    Low compression in cylinder 5

    A burnt exhaust valve, a collapsed lifter, a worn cam lobe, broken rings or a head gasket leak. Suspect it when spark and fuel test good, or when the misfire is present from cold and never changes.

  6. 6.

    Wiring or connector damage at the coil or injector for cylinder 5

    A chafed coil wire, a corroded injector connector or a pin backed out of the plug on that cylinder alone. Wiggle-test with the engine running.

  7. 7.

    Spark plug wire or distributor cap (older engines)

    On engines with plug wires, a cracked wire or a carbon-tracked cap terminal for cylinder 5 leaks spark to ground, especially in damp weather.

How to fix it: diagnosis, step by step

Cheapest and most likely checks first.

  1. 1 Read the codes and the freeze frame, then find cylinder 5

    Note the rpm, load and temperature when P0305 set: cold-only misfires lean toward injectors or compression, hot-only toward coils, load-only toward plugs and coils. Then confirm which cylinder is number 5 on your engine from a diagram before you touch anything; on many V engines the wrong bank is the easy one to reach.

  2. 2 Watch misfire counts in live data

    Most scan tools show a misfire counter per cylinder. Idle, then hold 2,000 rpm, then have a helper load the engine in gear with the brakes on. Counts that climb only under load say plug or coil; counts that climb only at idle say a leak or a leaking injector; steady counts everywhere say compression.

  3. 3 Pull spark plug 5 and read it

    Oil-wet means valve seals or rings, black and sooty means rich or a weak spark, white and blistered means lean or overheated, and a cracked insulator or a gap worn far past spec is the answer on its own. If the set is past its interval, replace all of them, gapped and torqued to spec.

  4. 4 Swap cylinder 5’s coil to a neighbor and clear the codes

    Move the coil (and its boot) from cylinder 5 to another cylinder and that cylinder’s coil to 5. Drive it. If the misfire moves with the coil, replace the coil. If it stays on 5, the coil is proven good and you move on. This is the single highest-value misfire test there is, and it costs nothing.

  5. 5 Test the injector

    With the engine idling, listen at the injector with a stethoscope or a long screwdriver for a steady click. Silence means no pulse (wiring or driver) or a stuck injector. Measure its resistance against the others, and on engines where injectors are easy to move, swap it the same way as the coil. On direct-injection engines, an injector balance test on the scan tool does the same job.

  6. 6 Check for a leak at that cylinder

    With the engine idling, spray carb cleaner or a propane stream around the intake runner and gasket for cylinder 5 and listen for an rpm change. A smoke machine on the intake shows the leak directly. Look at fuel trims: a lean trim that improves off idle supports a vacuum leak.

  7. 7 Run a compression or leak-down test on cylinder 5

    If spark, fuel and air all test good, measure compression on cylinder 5 and compare with its neighbors. More than about 10 to 15 percent below the rest points at valves, a lifter or cam lobe, rings or the head gasket; a leak-down test tells you which by where the air escapes: the intake, the exhaust, the crankcase or the coolant.

Known P0305 patterns by make

Brand-specific failure patterns from the field: find your make before parts-shopping.

Ford / Lincoln 2004–2008 F-150, Expedition, Navigator and 2005–2010 Mustang GT with the 5.4L and 4.6L 3-valve V8

Cylinder 5 is the front cylinder on the driver’s side. The 3-valve engines are famous for coil-on-plug failures and for two-piece spark plugs that seize and break off in the head on removal; Ford published a specific removal procedure with penetrating oil and a special extractor. Budget for the possibility of a broken plug when you pull number 5, and replace the coil boot with the coil. A misfire on these that comes with a startup rattle points at the cam phasers and timing components instead.

Nissan / Infiniti 2002–2008 Altima, Maxima, Murano, Quest and 2003–2007 G35, FX35, M35 with the VQ35DE V6

On the transverse VQ (Altima, Maxima, Murano, Quest) the odd cylinders 1, 3 and 5 are on the rear bank against the firewall, so cylinder 5 is the rear bank’s rearmost coil and the upper intake plenum usually has to come off to reach it. Coils fail when hot, and oil from a leaking valve cover or spark plug tube seal pools in the plug well and kills the coil and plug; fix the leak or the new coil dies too.

Chevrolet / GMC 2007–2014 Silverado, Sierra, Tahoe, Suburban, Yukon with the 5.3L V8 and Active Fuel Management

Cylinder 5 is the third cylinder back on the driver’s side. The 5.3’s well-known collapsed-lifter problem lives on the cylinders that Active Fuel Management shuts off, numbers 1, 4, 6 and 7; cylinder 5 is not one of them. So a lone P0305 on one of these trucks usually is the ordinary answer, a coil, a plug or an injector, and the swap test settles it. Oil consumption from stuck rings can foul a plug on any cylinder, so read plug 5 before condemning anything.

Parts & tools you may need

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Related codes

Frequently asked questions

What does code P0305 mean?
P0305 means the engine computer has detected repeated misfires on cylinder 5: the air and fuel in that cylinder are not burning when they should. It is serious. A steady light means fix it soon; a flashing light means unburned fuel is overheating the catalytic converter and you should stop driving.
Can I drive with P0305?
With a steady light, short and gentle trips to a shop are usually fine. With a flashing light, no: every mile of a flashing-light misfire dumps raw fuel into a converter that costs far more than any likely cause of the misfire. Many engines shut off fuel to the misfiring cylinder to protect it, which makes the shake worse but the damage less.
Where is cylinder 5 on my engine?
It depends on the engine family, not the car brand. Straight-six: the second cylinder from the firewall. Most V6s: the odd-numbered bank, often the rear bank on a transverse engine. GM small-block V8: the third cylinder back on the driver’s side. Ford modular V8: the front cylinder on the driver’s side. Chrysler V8: the third cylinder back on the driver’s side. Confirm with a diagram for your exact engine before you buy parts; our vehicle pages show the layout.
How do I know if it is the plug or the coil?
Swap cylinder 5’s coil with a neighbor and clear the codes. If the misfire follows the coil to the new cylinder, the coil is bad. If it stays on cylinder 5, the coil is fine: read the plug, then test the injector and compression. Replace the plug at the same time if it is anywhere near its interval.
Why is it only cylinder 5 and not the whole engine?
Because the parts that belong to one cylinder are the first suspects: its plug, its coil, its injector, its intake runner, its valves. A cause shared by all cylinders, such as fuel pressure or a big vacuum leak, usually sets P0300 or several cylinder codes at once. A lone P0305 points you at that one cylinder’s hardware.
How much does it cost to fix P0305?
A spark plug is $5 to $25, and a full set with labor is $100 to $350 depending on how buried they are. An ignition coil is $40 to $120 for the part, $100 to $250 installed. An injector is $80 to $300 installed on port-injected engines, more on direct injection. A compression cause (valve, lifter, head gasket) runs from a few hundred to a few thousand dollars, but it is the minority of cases.
Will P0305 clear itself?
The light can go out on its own if the misfire stops recurring for several drive cycles, which happens with a coil that only fails in the rain or a plug on the edge. The cause rarely heals. If P0305 returns after being cleared, something real is wrong with cylinder 5, and the swap test is the fastest way to find it.
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