P0304
High SeverityCylinder 4 Misfire Detected
Ignition System
P0304 — Instant Answer
Cylinder 4 Misfire Detected
Severity: HIGH SEVERITY
Meaning: Cylinder 4 is misfiring.
Safe to drive? NO if CEL is flashing. YES with caution if solid, but repair this week.
Estimated repair cost: $20 - $500
Most common causes:
- 1. Bad spark plug (35-45% of cases)
- 2. Faulty coil (35-45% of cases)
- 3. Bad injector (10-25% of cases)
- 4. Low compression (10-25% of cases)
Common Causes
How to Diagnose P0304
- 1Swap plug/coil to test
- 2Check injector
- 3Compression test
OEM Procedures for P0304
P0304 affects the Spark Plug. Found 116 OEM service manual procedures.
1969-73 PEUGEOT 504 4 Cylinder - Spark Plug Tube Replacement
1969-73 PEUGEOT 504 4 Cylinder - Spark Plug Tube Replacement
1969-73 PEUGEOT 504 4 Cylinder - Spark Plug Tube Replacement
1969-73 PEUGEOT 504 4 Cylinder - Spark Plug Tube Replacement
1969-73 PEUGEOT 504 4 Cylinder - Spark Plug Tube Replacement
1969-73 PEUGEOT 504 4 Cylinder - Spark Plug Tube Replacement
1969-73 PEUGEOT 504 4 Cylinder - Spark Plug Tube Replacement
1969-73 PEUGEOT 504 4 Cylinder - Spark Plug Tube Replacement
Showing 8 of 116 procedures
OEM Diagnostic Flowchart
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Related Resources
Repair guides, symptom pages, and wiring diagrams related to P0304.
OEM Manual Evidence
Browse →Mil Comes On With DTCS P0300 Thru P0306 (13-024) — 2013 Acura MDX 3.7L Eng VIN 2 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowl...
Mil Comes On With DTCS P0300 Thru P0306 (13-024) — 2013 Acura MDX 3.7L Eng VIN 2 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowl...
Mil Comes On With DTCS P0300 Thru P0306 (13-024) — 2013 Acura MDX 3.7L Eng VIN 2 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowl...
PGM-FI DTCS — 2013 Acura MDX 3.7L Eng VIN 2 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowledge Reimagined Home >> Acura >> 2013...
Exact Repair Workflows
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Open the exact repair flow most commonly associated with P0304 on this vehicle.
Open the exact repair flow most commonly associated with P0304 on this vehicle.
Open the exact repair flow most commonly associated with P0304 on this vehicle.
Open the exact repair flow most commonly associated with P0304 on this vehicle.
Open the exact repair flow most commonly associated with P0304 on this vehicle.
Related Symptoms
Browse →Rough idle often traces back to ignition, air metering, vacuum leaks, or timing-related faults before it becomes a full misfire complaint.
A check-engine light is a graph entry point into code pages, symptom-specific diagnosis, and the exact repair categories most often associated with those failures.
Exact Vehicle Hubs
Browse →Open the exact vehicle hub for a repair workflow commonly associated with P0304.
Open the exact vehicle hub for a repair workflow commonly associated with P0304.
Open the exact vehicle hub for a repair workflow commonly associated with P0304.
Open the exact vehicle hub grounded by OEM manual evidence related to P0304.
Open the exact vehicle hub for a repair workflow commonly associated with P0304.
Open the exact vehicle hub for a repair workflow commonly associated with P0304.
Related Codes
The engine is misfiring across multiple cylinders. This is often caused by something that affects all cylinders — spark plugs, fuel quality, vacuum leak, or low compression.
Cylinder 3 is misfiring.
Cylinder 5 is misfiring. Only on 5+ cylinder engines.
Frequently Asked Questions
- Can a vacuum leak cause a single cylinder misfire?
- If the leak is near one intake runner, yes. But usually vacuum leaks cause P0300 (random/multiple).
- What if new plugs and coils do not fix it?
- Check fuel injector operation and run a compression test. Low compression means valve or head gasket issue.
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Author & Review
Written by AllOEMManuals Editorial Team. Reviewed by ASE-certified technicians and updated with factory-reference checks for fitment-sensitive steps.
This guide was drafted with AI assistance and reviewed for accuracy by a human editor.
Last updated: 2026-05-07