The P0305 OBD-II trouble code means your vehicle’s engine control module has detected a misfire associated with Cylinder 5.
Because P0305 identifies one cylinder, diagnosis can be more focused than with P0300, which indicates random or multiple-cylinder misfires. However, P0305 does not automatically mean the Cylinder 5 ignition coil has failed.
A worn spark plug, weak ignition coil, defective fuel injector, damaged wire, intake leak, or mechanical compression problem can all trigger the same code. The computer knows Cylinder 5 isn’t contributing properly. It does not know which part deserves to be launched into the trash.
P0305 belongs to the misfire-code family covered in the complete Pro Street P-code OBD-II guide.
P0305 Quick Answer
| Item | Information |
|---|---|
| Trouble code | P0305 |
| Definition | Cylinder 5 Misfire Detected |
| System | Ignition and combustion |
| Severity | High |
| Safe to drive? | Only briefly if the misfire is mild and the Check Engine Light is not flashing |
| Most common causes | Spark plug, ignition coil, injector, wiring, vacuum leak, or low compression |
| Common symptoms | Rough idle, shaking, hesitation, power loss, and flashing Check Engine Light |
| Typical repair range | Approximately $30 to $5,000+, depending on the cause |
What Does the P0305 Code Mean?
P0305 breaks down as follows:
- P: Powertrain
- 0: Generic OBD-II code
- 3: Ignition or combustion misfire
- 05: Cylinder 5
Modern engine computers monitor changes in crankshaft speed during individual combustion events. Each properly operating cylinder accelerates the crankshaft slightly when it produces power.
When Cylinder 5 produces less power than expected, the crankshaft briefly slows. If the computer detects this pattern repeatedly, it stores P0305 and may turn on or flash the Check Engine Light.
P0305 identifies the affected cylinder, but it does not identify the failed component.
For a broader discussion of misfire behavior, causes, and warning signs, see our engine misfire symptoms and diagnosis guide.
Where Is Cylinder 5 Located?
Cylinder 5 location depends entirely on the engine and manufacturer.
P0305 normally applies to engines with at least five cylinders, including:
- Inline-five engines
- V6 engines
- Inline-six engines
- V8 engines
- V10 engines
- V12 engines
On an inline engine, the cylinders are positioned in a single row. On a V-engine, Cylinder 5 may be located on either cylinder bank depending on how the manufacturer numbers the engine.
For example, some manufacturers number cylinders sequentially along each bank. Others use odd-numbered cylinders on one bank and even-numbered cylinders on the other.
Do not assume Cylinder 5 is the fifth ignition coil you see.
Before disconnecting anything, verify the firing order and cylinder-numbering diagram using:
- Factory service information
- A manufacturer repair manual
- The underhood emissions label
- A reliable vehicle-specific firing-order diagram
Misidentifying Cylinder 5 can waste diagnostic time and may create an additional misfire if the wrong connector or coil is disturbed.
Common Symptoms of P0305
P0305 symptoms depend on how frequently Cylinder 5 misfires and under what operating conditions.
Common symptoms include:
- Check Engine Light
- Flashing Check Engine Light
- Rough idle
- Engine shaking
- Hesitation
- Poor acceleration
- Reduced engine power
- Hard starting
- Stalling
- Increased fuel consumption
- Raw fuel smell from the exhaust
- Excessive exhaust emissions
- Engine vibration under load
- Reduced turbo boost
- Limp mode
- Failed emissions test
An intermittent misfire may only appear during cold starts, idle, heavy acceleration, or high engine load.
A weak ignition coil, for example, may operate correctly at idle but fail when cylinder pressure increases under acceleration or boost.
How Serious Is P0305?
P0305 is a high-priority trouble code.
An active misfire can send unburned fuel into the exhaust system. That fuel may ignite inside the catalytic converter, generating enough heat to damage or melt the catalyst.
Continued driving may also cause:
- Catalytic converter failure
- Oxygen sensor contamination
- Cylinder-wall fuel wash
- Engine oil dilution
- Burned exhaust valves
- Piston damage
- Excessive engine vibration
- Damaged engine or transmission mounts
- Reduced fuel economy
- Increased emissions
Stop Driving Immediately If:
- The Check Engine Light is flashing
- The engine is shaking violently
- The vehicle has severe power loss
- The engine stalls repeatedly
- A strong raw-fuel smell is present
- The engine is overheating
- Mechanical knocking or valvetrain noise is heard
A flashing Check Engine Light generally indicates a catalyst-damaging misfire. Reduce engine load, pull over safely, and shut the engine off.
If the light remains steady and the engine runs relatively smoothly, driving a short distance for diagnosis may be possible. Avoid heavy throttle, high RPM, towing, and boost.
Most Common Causes of P0305
Cylinder 5 can misfire because of ignition, fuel, airflow, electrical, compression, or valve-timing problems.
| Possible cause | Relative likelihood |
| Worn or fouled spark plug | Very high |
| Weak or failed ignition coil | Very high |
| Damaged coil boot or spark plug wire | High |
| Clogged or failed fuel injector | High |
| Ignition coil wiring fault | Medium |
| Injector wiring fault | Medium |
| Intake manifold leak near Cylinder 5 | Medium |
| Low Cylinder 5 compression | Medium |
| Carbon buildup on an intake valve | Medium on direct-injected engines |
| Burned or leaking valve | Medium |
| Damaged piston ring | Lower |
| Valve spring, lifter, or camshaft problem | Lower |
| Head gasket failure | Lower |
| Incorrect valve timing | Lower |
| PCM driver failure | Rare |
Vehicle design, mileage, maintenance history, and freeze-frame conditions should determine which cause is tested first.
Tools Needed to Diagnose P0305
Useful diagnostic tools include:
- OBD-II scanner
- Scan tool with live misfire counters
- Digital multimeter
- Spark tester
- Spark plug socket
- Compression tester
- Cylinder leak-down tester
- Noid light
- Mechanic’s stethoscope
- Smoke machine
- Fuel-pressure gauge
- Borescope
- Vehicle-specific wiring diagram
- Factory service information
A basic scanner can retrieve P0305. A professional scan tool may also display individual-cylinder misfire counters, Mode $06 test results, injector commands, fuel trims, and freeze-frame information.
How to Diagnose P0305
Step 1: Confirm P0305
Connect the scan tool and record:
- Stored codes
- Pending codes
- Permanent codes
- Freeze-frame data
- Individual-cylinder misfire counts
Do not clear the code before recording the freeze-frame information.
Important data includes:
- Engine RPM
- Engine load
- Vehicle speed
- Coolant temperature
- Intake-air temperature
- Short-term fuel trim
- Long-term fuel trim
- Throttle position
- Fuel-system status
The conditions under which P0305 appeared can narrow the search.
| When P0305 occurs | Possible diagnostic direction |
| Cold start | Injector leak, carbon buildup, coolant intrusion, or weak compression |
| Warm idle | Vacuum leak, injector imbalance, or compression problem |
| Heavy acceleration | Weak coil, worn plug, excessive plug gap, or fuel-delivery problem |
| Wet weather | Coil boot, plug wire, or connector insulation |
| Constantly | Dead coil, failed injector, wiring fault, or mechanical damage |
| After recent service | Disconnected connector, wrong plug gap, damaged wire, or incorrect installation |
Step 2: Check for Related Codes
P0305 may appear with other misfire, fuel, ignition, or sensor codes.
Related codes can include:
- P0300 — Random or Multiple Cylinder Misfire
- P0301 — Cylinder 1 Misfire
- P0302 — Cylinder 2 Misfire
- P0303 — Cylinder 3 Misfire
- P0304 — Cylinder 4 Misfire
- P0306 — Cylinder 6 Misfire
- P0171 or P0174 — System Too Lean
- P0172 or P0175 — System Too Rich
- P0205 — Cylinder 5 Injector Circuit Malfunction
- P0355 — Ignition Coil E Primary/Secondary Circuit Malfunction
- Crankshaft or camshaft position codes
Several cylinders misfiring together may point toward a shared problem such as:
- Low fuel pressure
- Contaminated fuel
- Large vacuum leak
- MAF sensor error
- Incorrect valve timing
- Charging-system problem
- Poor engine ground
- Crankshaft position signal fault
Step 3: Verify Cylinder 5 Location
Use reliable vehicle-specific information to identify Cylinder 5.
Once located, inspect the surrounding area for:
- Disconnected coil or injector connectors
- Loose connector terminals
- Oil inside the spark plug well
- Coolant contamination
- Damaged wiring
- Rodent damage
- Cracked vacuum hoses
- Loose grounds
- Intake manifold leaks
- Harnesses touching hot exhaust components
If P0305 appeared immediately after a tune-up or engine repair, begin with a visual inspection. Many post-repair misfires are caused by a connector that never fully latched or a coil boot that was damaged during installation.
Step 4: Inspect the Cylinder 5 Spark Plug
Remove the Cylinder 5 spark plug and compare it with a plug from a healthy cylinder.
Look for:
- Worn electrodes
- Excessive gap
- Cracked porcelain
- Carbon fouling
- Oil contamination
- Wet fuel deposits
- Coolant deposits
- Overheating
- Incorrect plug type
- Improper installation
A fuel-wet spark plug may indicate that the injector is delivering fuel but the cylinder lacks spark.
A dry plug may suggest insufficient fuel delivery.
Heavy oil deposits may indicate worn rings, valve-guide problems, a leaking tube seal, or a PCV-related issue.
If the plugs are worn beyond the manufacturer’s service interval, replace the complete set using the correct part number and gap.
Step 5: Swap the Cylinder 5 Ignition Coil
On a coil-on-plug engine, move the Cylinder 5 ignition coil to another cylinder.
For example, swap the Cylinder 5 and Cylinder 3 coils. Clear the codes and operate the engine under conditions similar to those recorded in the freeze-frame data.
If the code changes from:
P0305 to P0303
the ignition coil is likely defective.
If P0305 returns on Cylinder 5, the coil is probably not the cause.
Inspect the coil and boot for:
- Carbon tracking
- Cracks
- Oil contamination
- Moisture
- Corroded terminals
- Burned internal springs
- Damaged insulation
Our ignition coil replacement guide explains how to inspect and replace coils without automatically condemning the entire set.
Engines using distributor ignition, coil packs, or spark plug wires require different testing. Inspect wire resistance, insulation, routing, and coil output using the appropriate service procedure.
Step 6: Test the Cylinder 5 Fuel Injector
A clogged, leaking, stuck, electrically open, or unpowered injector can trigger P0305.
Start by listening to the injector with a mechanic’s stethoscope. Compare the clicking sound from Cylinder 5 with the other cylinders.
Further testing may include:
- Injector resistance measurement
- Injector voltage test
- Noid-light test
- Injector current-ramp test
- Injector balance test
- Fuel-pressure drop test
- Injector swap test where practical
Injector resistance specifications vary significantly. Use factory specifications instead of assuming every injector should produce the same generic resistance value.
Pro Street injector testing references include:
- How to Test a Ford Ranger Fuel Injector
- How to Test Nissan Altima Fuel Injectors
- How to Test a Toyota Corolla Fuel Injector
- How to Test an Acura RSX Fuel Injector
Never loosen a gasoline direct-injection or diesel common-rail fuel connection without following the manufacturer’s pressure-relief procedure. These systems can retain dangerously high pressure after the engine is shut off.
Step 7: Inspect the Ignition and Injector Circuits
If the Cylinder 5 coil and injector test correctly, inspect their electrical circuits.
Check for:
- Correct supply voltage
- Reliable ground
- Ignition-coil trigger signal
- Injector control pulse
- Loose terminal tension
- Corroded connector pins
- High circuit resistance
- Wiring shorted to voltage
- Wiring shorted to ground
- Harness damage
- Poor engine or PCM grounds
Perform voltage-drop testing with the circuit operating whenever possible.
A wire can pass a basic continuity test while failing under electrical load. Continuity alone is not a lifetime achievement award for wiring.
PCM failure is possible, but it is rare. Verify the component, wiring, power supply, grounds, and mechanical condition before condemning the control module.
Step 8: Check for an Intake or Vacuum Leak
An intake leak near the Cylinder 5 runner can create a localized lean condition.
Inspect:
- Intake manifold gasket
- Cylinder 5 injector seal
- Vacuum hoses
- PCV system
- Brake-booster hose
- Intake manifold
- Throttle-body gasket
A smoke test is generally the safest and most accurate way to locate an intake-system leak.
Fuel-trim data can also help. Strongly positive fuel trim at idle that improves when engine speed increases frequently indicates a vacuum leak.
Step 9: Perform a Compression Test
If Cylinder 5 has spark, fuel, and proper electrical control, test its compression.
Compare Cylinder 5 with the remaining cylinders. Use manufacturer specifications for minimum pressure and allowable variation.
Low compression may result from:
- Burned intake valve
- Burned exhaust valve
- Bent valve
- Worn piston rings
- Damaged piston
- Broken valve spring
- Collapsed lifter
- Worn camshaft lobe
- Head gasket failure
- Cylinder-wall damage
- Incorrect valve timing
A wet compression test may help distinguish piston-ring leakage from a valve problem. A cylinder leak-down test provides more specific information.
Step 10: Perform a Cylinder Leak-Down Test
Position Cylinder 5 at top dead center on its compression stroke and introduce regulated compressed air.
Listen for escaping air:
| Air heard or observed at | Likely fault |
| Throttle body or intake | Leaking intake valve |
| Exhaust outlet | Leaking exhaust valve |
| Oil filler opening | Piston rings or cylinder damage |
| Cooling system | Head gasket, cylinder head, or block damage |
| Adjacent cylinder | Head gasket failure between cylinders |
Leak-down testing is especially important when P0305 remains on Cylinder 5 after the plug, coil, injector, and wiring have passed inspection.
Step 11: Check for Intake-Valve Carbon Buildup
Gasoline direct-injection engines can accumulate deposits on their intake valves because fuel is injected directly into the cylinder instead of washing across the back of the valve.
Uneven buildup around Cylinder 5 may cause:
- Cold-start misfire
- Rough idle
- Airflow imbalance
- P0305 that improves after warm-up
A borescope inspection can help verify deposit buildup.
Approved cleaning methods vary by manufacturer and may include media blasting or professional chemical cleaning. A fuel-tank additive generally cannot clean a direct-injected intake valve because the fuel never contacts it. Marketing departments hate this one simple fact.
Step 12: Clear P0305 and Confirm the Repair
After repairing the verified fault:
- Clear stored and pending codes.
- Start the engine.
- Verify a smooth idle.
- Monitor Cylinder 5 misfire counters.
- Recreate the original freeze-frame conditions when safe.
- Complete the manufacturer’s drive cycle.
- Scan for pending and permanent codes.
- Confirm that readiness monitors complete normally.
A successful repair means the misfire counters remain normal and P0305 does not return under the original operating conditions.
Common P0305 Repairs and Costs
Actual prices depend on the vehicle, labor rate, component accessibility, and underlying failure.
| Repair | Approximate installed cost |
| Replace spark plugs | $50–$500 |
| Replace one ignition coil | $80–$450 |
| Replace plug wire or coil boot | $30–$250 |
| Clean or replace one injector | $150–$1,000 |
| Repair wiring or connector | $100–$700 |
| Repair intake or vacuum leak | $100–$900 |
| Intake-valve carbon cleaning | $400–$1,500 |
| Replace intake manifold gasket | $300–$1,500 |
| Cylinder-head or valve repair | $1,500–$5,000+ |
| Engine replacement | $4,000–$15,000+ |
The same P0305 code can be caused by a worn spark plug or a burned valve. Test first. Price the repair second.
Common P0305 Diagnostic Mistakes
Replacing the Coil Without Swap-Testing It
A weak coil is common, but P0305 does not prove the coil has failed. Move it to another cylinder and see whether the misfire follows.
Testing the Wrong Cylinder
Verify the engine’s cylinder-numbering layout before removing components. This is especially important on V6, V8, V10, and V12 engines.
Ignoring the Spark Plug
A new ignition coil will not repair a cracked, oil-fouled, incorrectly gapped, or worn spark plug.
Replacing the Injector Without Testing It
Confirm injector power, control, resistance, and fuel delivery before replacement.
Clearing Freeze-Frame Data Too Early
Clearing the code erases valuable information about when and how the misfire occurred.
Skipping Compression Testing
If the plug, coil, injector, and wiring are working, stop replacing parts and check the mechanical condition of Cylinder 5.
Replacing the Catalytic Converter First
A damaged catalytic converter may be a consequence of P0305 rather than its original cause. Repair the misfire before evaluating catalyst performance.
P0305 Frequently Asked Questions
Does P0305 Mean Ignition Coil 5 Is Bad?
No. The ignition coil is a common cause, but a spark plug, injector, wiring fault, intake leak, or compression problem can also trigger P0305.
Can a Bad Spark Plug Cause P0305?
Yes. A worn, fouled, cracked, or incorrectly gapped Cylinder 5 spark plug is one of the most common causes.
Can a Fuel Injector Cause P0305?
Yes. A clogged, leaking, stuck, electrically failed, or unpowered Cylinder 5 injector can create a cylinder-specific misfire.
Can P0355 Cause P0305?
Yes. P0355 indicates an electrical malfunction associated with the Ignition Coil E circuit, which commonly corresponds with Cylinder 5 on many applications. Always verify the manufacturer’s coil designation and wiring diagram.
Can a Vacuum Leak Affect Only Cylinder 5?
Yes. A leaking intake manifold gasket or injector seal near the Cylinder 5 intake runner may create a localized lean condition.
Can Low Compression Cause P0305?
Yes. Burned valves, worn rings, piston damage, valvetrain faults, or a head gasket failure can reduce Cylinder 5 compression.
Why Does P0305 Only Appear During Acceleration?
Higher cylinder pressure requires more ignition voltage. A weak coil, worn plug, excessive plug gap, or fuel-delivery problem may only cause a misfire under load.
Why Does P0305 Appear Only During a Cold Start?
Possible causes include a leaking injector, intake-valve deposits, coolant intrusion, low compression, or a temperature-sensitive electrical fault.
Can I Drive With P0305?
Only for a short distance if the engine runs reasonably smoothly and the Check Engine Light remains steady. Stop driving if the light flashes, the engine shakes severely, power drops dramatically, or raw fuel can be smelled.
Can P0305 Damage the Catalytic Converter?
Yes. Unburned fuel can overheat and destroy the catalytic converter, especially when the Check Engine Light is flashing.
Will P0305 Clear Itself?
The Check Engine Light may turn off after several successful drive cycles if the misfire does not return. Stored or permanent code data may remain until the required self-tests are completed.
Related Misfire and Ignition Codes
- P0300 — Random or Multiple Cylinder Misfire
- P0301 — Cylinder 1 Misfire
- P0302 — Cylinder 2 Misfire
- P0303 — Cylinder 3 Misfire
- P0304 — Cylinder 4 Misfire
- P0305 — Cylinder 5 Misfire
- P0306 — Cylinder 6 Misfire
- P0307 — Cylinder 7 Misfire
- P0308 — Cylinder 8 Misfire
- P0316 — Misfire Detected During Startup
- P0205 — Cylinder 5 Injector Circuit Malfunction
- P0355 — Ignition Coil E Primary/Secondary Circuit Malfunction
Explore the Pro Street OBD-II Code Libraries
Use the Pro Street cornerstone guides to find additional diagnostic trouble codes:
- All P OBD-II Codes Explained — Powertrain Codes
- All B OBD-II Codes Explained — Body and SRS Codes
- All C OBD-II Codes Explained — Chassis Codes
- OBD-II DTC Doctor
P0305 tells you that Cylinder 5 is misfiring. It does not tell you to replace the coil, injector, catalytic converter, or half the engine before lunch.
Start with the freeze-frame data, verify the correct cylinder, and inspect the plug. Swap-test the ignition coil, test the injector and wiring, inspect for intake leaks, and verify compression before purchasing parts.
