The P0308 OBD-II trouble code means the engine control module has detected a misfire associated with Cylinder 8.
Unlike P0300, which indicates random or multiple-cylinder misfires, P0308 identifies one specific cylinder. That makes diagnosis more focused, but it does not prove the Cylinder 8 ignition coil has failed.
A worn spark plug, weak coil, failed fuel injector, damaged circuit, intake leak, low compression, valve problem, or coolant intrusion can all trigger P0308.
The computer knows Cylinder 8 failed to contribute the expected power. It does not know which component should be replaced. Apparently, the parts cannon remains an aftermarket accessory rather than an approved diagnostic tool.
P0308 belongs to the misfire family covered in the complete Pro Street P-code OBD-II guide.
P0308 Quick Answer
| Item | Information |
|---|---|
| Trouble code | P0308 |
| Definition | Cylinder 8 Misfire Detected |
| System | Ignition and combustion |
| Severity | High |
| Safe to drive? | Only briefly if the engine runs smoothly and the Check Engine Light is not flashing |
| Most common causes | Spark plug, ignition coil, injector, wiring, intake leak, or low compression |
| Common applications | V8, V10, V12 and W12 engines |
| Related codes | P0208, P0358 and P0300 |
| Typical repair range | Approximately $30 to $7,000+, depending on the cause |
What Does the P0308 Code Mean?
P0308 breaks down as follows:
- P: Powertrain
- 0: Generic OBD-II code
- 3: Ignition or combustion misfire
- 08: Cylinder 8
The engine control module monitors small changes in crankshaft speed during each combustion event. Every healthy cylinder accelerates the crankshaft slightly when combustion pushes its piston downward.
When Cylinder 8 repeatedly produces less power than expected, the crankshaft slows momentarily. The computer recognizes that pattern, stores P0308, and may illuminate or flash the Check Engine Light.
P0308 identifies the affected cylinder. It does not determine whether the failure involves:
- Spark
- Fuel delivery
- Airflow
- Compression
- Valve operation
- Mechanical timing
- Electrical control
For a broader explanation of combustion failures, visit our engine misfire symptoms, causes and diagnosis guide.
Where Is Cylinder 8 Located?
P0308 applies to engines with at least eight cylinders, including:
- V8 engines
- V10 engines
- V12 engines
- W12 engines
- Other specialty multi-cylinder engines
Cylinder 8 location depends on the manufacturer and engine family.
Some manufacturers place odd-numbered cylinders on one bank and even-numbered cylinders on the other. Others number cylinders sequentially along each bank.
Cylinder 8 may be located:
- At the rear of one cylinder bank
- At the front of the opposite bank
- On the driver or passenger side
- Beneath an intake duct, cowl, wiring harness, or other obstruction
Do not assume Cylinder 8 is the eighth ignition coil you happen to see.
Verify its location using:
- Factory service information
- Manufacturer repair manual
- Underhood emissions label
- Vehicle-specific firing-order diagram
- Correct engine identification code
This is especially important when a vehicle model is available with several V8 engines that use different ignition systems or cylinder-numbering conventions.
Why Cylinder 8 Can Be Difficult to Diagnose
Cylinder 8 is frequently positioned near the rear of a V8 engine, although that is not universal.
A rear-cylinder location can create practical diagnostic challenges:
- Limited access to the spark plug
- Restricted ignition-coil removal
- Wiring routed close to exhaust components
- Heat-damaged connectors
- Oil or coolant collecting near the plug well
- Intake manifold leaks near the rear runner
- Cowl or HVAC components blocking access
- Poor visibility during inspection
Limited access is not proof of failure, but it can allow damage, corrosion, contamination, or loose connections to remain hidden.
Before condemning the coil or injector, inspect the complete Cylinder 8 area with a light and mirror or borescope.
Common Conditions Associated With P0308
A Cylinder 8 combustion problem may cause:
- Illuminated Check Engine Light
- Flashing Check Engine Light
- Rough or unstable idle
- Engine shaking
- Hesitation
- Poor acceleration
- Reduced engine power
- Hard starting
- Stalling
- Increased fuel consumption
- Raw fuel smell from the exhaust
- Failed emissions test
- Popping from the intake or exhaust
- Reduced turbo or supercharger boost
- Limp mode
- Additional ignition, injector, or fuel-trim codes
An intermittent P0308 may only appear during:
- Cold starts
- Warm idle
- Heavy acceleration
- High engine load
- Wet weather
- Extended highway driving
- Heat soak after shutdown
The freeze-frame data stored with P0308 can help identify which condition should be recreated during testing.
How Serious Is P0308?
P0308 should be treated as a high-priority trouble code.
An active misfire may send unburned fuel into the exhaust. That fuel can ignite inside the catalytic converter, creating enough heat to damage or melt the catalyst.
Continued driving may also contribute to:
- 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 shakes violently
- Power loss is severe
- The vehicle stalls
- A strong raw-fuel smell is present
- The engine overheats
- Mechanical knocking is heard
- Abnormal valvetrain noise develops
A flashing Check Engine Light generally indicates a catalyst-damaging misfire. Reduce engine load, pull over safely, and shut off the engine.
If the light remains steady and the engine runs reasonably smoothly, driving a short distance for diagnosis may be possible. Avoid heavy throttle, high RPM, towing, and boost.
Most Common Causes of P0308
Cylinder 8 can misfire because of an ignition, fuel, airflow, electrical, compression, or mechanical problem.
| 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 |
| Coil or injector wiring fault | Medium |
| Intake manifold leak near Cylinder 8 | Medium |
| Low Cylinder 8 compression | Medium |
| Oil or coolant in the spark plug well | Application dependent |
| Carbon buildup on an intake valve | Medium on direct-injected engines |
| Burned or leaking valve | Medium |
| Coolant intrusion into Cylinder 8 | Application dependent |
| Worn camshaft lobe or failed lifter | Application dependent |
| Damaged piston ring | Lower |
| Head gasket failure | Lower |
| Incorrect valve timing | Lower |
| PCM driver failure | Rare |
The vehicle, engine family, mileage, service history, companion codes, and freeze-frame conditions should determine the testing order.
How to Diagnose P0308
Step 1: Confirm P0308
Connect an OBD-II scanner and record:
- Stored codes
- Pending codes
- Permanent codes
- Freeze-frame data
- Individual-cylinder misfire counters
Do not clear the code before saving the freeze-frame information.
Record:
- 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 operating conditions provide useful clues.
| When P0308 occurs | Possible direction |
| Cold start | Injector leak, deposits, coolant intrusion, or weak compression |
| Warm idle | Intake leak, injector imbalance, or mechanical problem |
| Heavy acceleration | Weak coil, worn plug, excessive plug gap, or insufficient fuel |
| Wet weather | Coil boot, plug wire, or damaged insulation |
| After heat soak | Ignition coil, injector, connector, or wiring fault |
| Constantly | Dead coil, failed injector, circuit problem, or low compression |
| After recent service | Loose connector, damaged boot, wrong plug, or installation error |
Step 2: Check for Related Codes
P0308 may appear with other misfire, ignition, fuel, cooling-system, or valvetrain codes.
Related codes include:
- P0300 — Random or Multiple Cylinder Misfire
- P0301 — Cylinder 1 Misfire
- P0302 — Cylinder 2 Misfire
- P0304 — Cylinder 4 Misfire
- P0305 — Cylinder 5 Misfire
- P0306 — Cylinder 6 Misfire
- P0307 — Cylinder 7 Misfire
- P0171 or P0174 — System Too Lean
- P0172 or P0175 — System Too Rich
- P0208 — Cylinder 8 Injector Circuit Malfunction
- P0358 — Ignition Coil H Primary/Secondary Circuit Malfunction
- Camshaft or crankshaft position codes
- Coolant-temperature or overheating codes
Several cylinders misfiring together may indicate a shared failure 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 8 Location
Use vehicle-specific service information to identify Cylinder 8.
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
- Intake manifold leaks
- Harnesses contacting exhaust components
- Loose engine grounds
Pay close attention to wiring routed near the exhaust manifold or cylinder head. Repeated heating and cooling can make insulation brittle and damage connector locks.
If P0308 appeared after maintenance, verify that the correct spark plug, coil and injector connectors are installed and fully seated.
Step 4: Inspect the Cylinder 8 Spark Plug
Remove the Cylinder 8 spark plug and compare it with a plug from a healthy cylinder.
Check for:
- Worn electrodes
- Excessive gap
- Cracked porcelain
- Carbon fouling
- Oil contamination
- Wet fuel deposits
- Coolant deposits
- Overheating
- Incorrect heat range
- Wrong plug type
- Improper torque
A fuel-wet plug may indicate that fuel is reaching Cylinder 8 but ignition is missing.
A dry plug may suggest inadequate fuel delivery.
Oil deposits may point toward:
- Worn piston rings
- Valve-guide problems
- PCV-system failure
- Leaking spark plug tube seal
- Oil entering the plug well
Unusual white or steam-cleaned deposits may justify checking for coolant intrusion.
If the plugs have exceeded their service interval, replace the complete set using the correct specification and gap.
Step 5: Swap the Cylinder 8 Ignition Coil
If the engine uses coil-on-plug ignition, move the Cylinder 8 coil to another cylinder.
For example, swap the Cylinder 8 and Cylinder 6 coils. Clear the codes and operate the engine under conditions similar to the original freeze-frame data.
If the code changes from:
P0308 to P0306
the ignition coil is likely defective.
If P0308 returns on Cylinder 8, the coil probably is not the cause.
Inspect the coil and boot for:
- Carbon tracking
- Cracks
- Moisture
- Oil contamination
- Coolant contamination
- Corroded contacts
- Burned internal springs
- Damaged insulation
Review our bad ignition coil guide for additional information about ignition-coil testing and failure patterns.
Also see our ignition coil replacement guide before installing replacement components.
Engines using distributor ignition, coil packs, or spark plug wires require different testing. Check wire resistance, routing, insulation, and coil output using factory procedures.
Step 6: Understand P0308 Versus P0358
P0308 and P0358 describe related but different problems.
| Code | Meaning |
| P0308 | The PCM detected a combustion misfire associated with Cylinder 8 |
| P0358 | The PCM detected an electrical malfunction involving Ignition Coil H’s primary or secondary circuit |
P0358 provides stronger evidence of an ignition-coil circuit failure.
Possible P0358 causes include:
- Failed ignition coil
- Missing coil power
- Open trigger circuit
- Trigger circuit shorted to ground
- Trigger circuit shorted to voltage
- Loose connector terminal
- Corroded connector
- Damaged wiring
- Failed PCM coil driver
P0308 without P0358 may still be caused by ignition, but fuel delivery, compression, airflow, and mechanical operation must also be tested.
Coil letters often correspond with cylinder numbers, but verify the manufacturer’s coil designation before assuming Coil H controls Cylinder 8.
Step 7: Test the Cylinder 8 Fuel Injector
A clogged, leaking, stuck, electrically open, or unpowered injector can cause P0308.
Listen to the Cylinder 8 injector with a mechanic’s stethoscope and compare its sound with the remaining injectors.
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
Use manufacturer specifications for injector resistance and circuit testing.
Pro Street injector-testing resources 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 open a gasoline direct-injection or diesel common-rail fuel system without following the manufacturer’s pressure-relief procedure.
Step 8: Understand P0308 Versus P0208
P0208 indicates an electrical fault involving the Cylinder 8 fuel-injector circuit.
| Code | Meaning |
| P0308 | Cylinder 8 combustion misfire |
| P0208 | Cylinder 8 injector circuit malfunction |
If P0308 and P0208 appear together, concentrate on:
- Injector power supply
- Injector control circuit
- Connector condition
- Terminal tension
- Injector resistance
- Wiring continuity under load
- PCM injector driver
P0208 does not automatically prove the injector itself has failed. Damaged wiring or a connector problem can prevent a good injector from operating.
Step 9: Inspect the Coil and Injector Circuits
If the coil and injector test correctly, inspect their circuits.
Check for:
- Correct supply voltage
- Reliable ground
- Ignition-coil trigger signal
- Injector control pulse
- Loose terminal tension
- Corroded pins
- High circuit resistance
- Wiring shorted to ground
- Wiring shorted to voltage
- Heat-damaged insulation
- Poor engine or PCM grounds
Use voltage-drop testing while the circuit is operating whenever possible.
A wire can pass a continuity test while failing under electrical load. The multimeter beep is helpful, but it is not a notarized statement of innocence.
PCM failure is possible but uncommon. Verify the component, wiring, power supply, grounds, and mechanical condition before replacing a control module.
Step 10: Check for an Intake Leak
An intake leak near the Cylinder 8 runner may create a localized lean condition.
Inspect:
- Intake manifold gasket
- Cylinder 8 injector seal
- Vacuum hoses
- PCV system
- Brake-booster hose
- Intake manifold
- Throttle-body gasket
A smoke test is generally the safest and most effective way to locate an intake leak.
Fuel-trim data may provide another clue. Strongly positive fuel trim at idle that improves as engine speed increases frequently points toward a vacuum leak.
Step 11: Check for Coolant Intrusion
Coolant entering Cylinder 8 may cause a cold-start misfire that improves as the engine warms.
Possible sources include:
- Head gasket failure
- Cracked cylinder head
- Intake manifold gasket failure on applicable engines
- Internal coolant passage leak
Warning signs include:
- Unexplained coolant loss
- White exhaust vapor after warm-up
- Sweet exhaust smell
- Steam-cleaned Cylinder 8 spark plug
- Cooling-system pressure remaining after a cold soak
- P0308 occurring primarily after the vehicle sits overnight
- Bubbles in the coolant reservoir
- Cylinder 8 showing unusually clean piston deposits
A cooling-system pressure test, borescope inspection, combustion-gas test, compression test, and leak-down test may be necessary.
Do not open a hot cooling system. Pressurized coolant remains remarkably committed to escaping in the least pleasant direction available.
Step 12: Perform a Compression Test
If Cylinder 8 has spark, fuel, and correct electrical control, test its compression.
Compare Cylinder 8 with the remaining cylinders and follow manufacturer specifications for minimum pressure and allowable variation.
Low compression may be caused by:
- 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
If Cylinder 8 compression is low, continue with a cylinder leak-down test.
Step 13: Perform a Cylinder Leak-Down Test
Position Cylinder 8 at top dead center on its compression stroke and introduce regulated compressed 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 helps distinguish an electrical or fuel-delivery problem from internal engine damage.
Step 14: Inspect Cylinder 8 Valve Operation
If compression is low or valvetrain noise is present, inspect valve movement.
Depending on the engine, testing may include:
- Removing the valve cover
- Comparing rocker-arm movement
- Measuring valve lift
- Inspecting pushrods
- Checking valve springs
- Inspecting lifters
- Verifying engine oil pressure
- Inspecting the camshaft with a borescope
- Checking the oil filter for metal debris
Reduced valve lift on Cylinder 8 may indicate a failed lifter, damaged rocker arm, or worn camshaft lobe.
Step 15: Check for Intake-Valve Deposits
Direct-injected engines can develop deposits on their intake valves because fuel no longer washes across the back of each valve.
Uneven deposits near Cylinder 8 may cause:
- Cold-start P0308
- Rough idle
- Airflow imbalance
- Misfire that improves after warm-up
A borescope inspection can help confirm deposit buildup. Approved cleaning methods vary by manufacturer and may include media blasting or professional chemical cleaning.
Step 16: Clear P0308 and Verify the Repair
After repairing the confirmed fault:
- Clear stored and pending codes.
- Start the engine.
- Verify a stable idle.
- Monitor Cylinder 8 misfire counters.
- Recreate the original freeze-frame conditions when safe.
- Complete the required drive cycle.
- Scan for pending codes.
- Confirm that readiness monitors complete normally.
The repair is confirmed when Cylinder 8 misfire counts remain normal and P0308 does not return.
Common P0308 Repairs and Costs
Actual costs depend on the vehicle, labor rate, accessibility, and underlying failure.
| Repair | Approximate installed cost |
| Replace spark plugs | $50–$600 |
| Replace one ignition coil | $80–$500 |
| Replace plug wire or coil boot | $30–$300 |
| Clean or replace one injector | $150–$1,200 |
| Repair wiring or connector | $100–$800 |
| Repair intake or vacuum leak | $100–$1,000 |
| Intake-valve carbon cleaning | $400–$1,500 |
| Replace intake manifold gasket | $400–$1,800 |
| Repair coolant intrusion | $500–$6,000+ |
| Replace failed lifter or camshaft | $1,500–$7,000+ |
| Cylinder-head or valve repair | $1,500–$6,000+ |
| Engine replacement | $5,000–$20,000+ |
P0308 can represent anything from a worn spark plug to internal engine damage. Diagnose the cause before estimating the repair.
Common P0308 Diagnostic Mistakes
Replacing Coil 8 Without Testing It
Swap the Cylinder 8 coil with another cylinder. If the misfire follows the coil, replace it. If P0308 remains, continue testing.
Testing the Wrong Cylinder
Cylinder numbering varies among V8, V10 and V12 engines. Verify the correct layout before removing components.
Confusing P0308 With P0358
P0308 is a combustion-misfire code. P0358 identifies an electrical problem involving Ignition Coil H’s circuit.
Ignoring P0208
P0308 combined with P0208 strongly suggests an injector or injector-circuit problem that deserves priority testing.
Ignoring Coolant Loss
A cold-start P0308 combined with unexplained coolant loss may indicate internal coolant intrusion.
Overlooking Rear-Cylinder Wiring
Heat, limited access and tight harness routing can damage Cylinder 8 wiring and connectors.
Replacing the Injector Without Testing It
Confirm injector power, control and fuel delivery before replacement.
Clearing Freeze-Frame Data Too Early
Freeze-frame information may be the best evidence of when and how P0308 occurred.
Skipping Compression Testing
If the plug, coil, injector and circuits test correctly, verify the mechanical condition of Cylinder 8.
Replacing the Catalytic Converter First
The converter may have been damaged by the misfire. Correct P0308 before evaluating catalyst performance.
P0308 Frequently Asked Questions
Does P0308 Mean the Cylinder 8 Ignition Coil Is Bad?
No. A failed coil is common, but P0308 may also result from a spark plug, injector, wiring, intake leak, compression problem, coolant intrusion, or valvetrain failure.
Can P0358 Cause P0308?
Yes. P0358 identifies an electrical malfunction involving Ignition Coil H, which commonly corresponds with Cylinder 8. Verify the manufacturer’s coil assignment before testing.
Can P0208 Cause P0308?
Yes. If the Cylinder 8 injector circuit fails, Cylinder 8 may not receive the correct amount of fuel and can misfire.
Can a Spark Plug Cause P0308?
Yes. A worn, cracked, fouled, overheated, or incorrectly gapped Cylinder 8 spark plug is one of the most common causes.
Can a Fuel Injector Cause P0308?
Yes. A clogged, leaking, stuck, electrically failed, or unpowered Cylinder 8 injector can cause a cylinder-specific misfire.
Can an Intake Leak Affect Only Cylinder 8?
Yes. An intake manifold gasket or injector-seal leak near the Cylinder 8 runner may create a localized lean condition.
Can Coolant Entering Cylinder 8 Cause P0308?
Yes. A head gasket, cylinder head, or intake manifold gasket leak can allow coolant into Cylinder 8 and produce a cold-start misfire.
Can Low Compression Cause P0308?
Yes. Burned valves, worn rings, piston damage, valvetrain faults, or head gasket failure can reduce Cylinder 8 compression.
Why Does P0308 Only Appear During Acceleration?
A weak coil, worn plug, excessive plug gap, restricted injector, or fuel-pressure problem may only become noticeable as cylinder pressure and engine load increase.
Why Does P0308 Appear After the Engine Sits Overnight?
Possible causes include a leaking injector, coolant intrusion, oil entering the plug well, intake-valve deposits, or a temperature-sensitive electrical problem.
Can I Drive With P0308?
Only briefly 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, or raw fuel can be smelled.
Can P0308 Damage the Catalytic Converter?
Yes. Unburned fuel can overheat and destroy the catalytic converter.
Will P0308 Clear Itself?
The Check Engine Light may turn off after several successful drive cycles, but stored or permanent code data can remain until the required self-tests are completed.
Related Misfire, Injector 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
- P0208 — Cylinder 8 Injector Circuit Malfunction
- P0358 — Ignition Coil H Primary/Secondary Circuit Malfunction
Explore the Pro Street OBD-II Code Libraries
Use the Pro Street cornerstone pages 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
P0308 identifies a misfire associated with Cylinder 8. Begin by saving the freeze-frame data and confirming the correct cylinder location.
Inspect the spark plug, swap-test the ignition coil, and test the injector and related circuits. If the misfire remains on Cylinder 8, inspect for intake leaks, coolant intrusion, low compression, and valvetrain problems.
The objective is not to replace the most popular suspect. It is to prove which system failed and verify that P0308 stays gone.
