P0303
High SeverityCylinder 3 Misfire Detected
Ignition System
P0303 — Instant Answer
Cylinder 3 Misfire Detected
Severity: HIGH SEVERITY
Meaning: Cylinder 3 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)
Symptoms
- ⚠️Rough idle
- ⚠️Power loss
- ⚠️Check engine light
- ⚠️Vibration
Related Symptoms
Common Causes
How to Diagnose P0303
- 1Swap plug/coil to test
- 2Check injector
- 3Compression test
OEM Procedures for P0303
P0303 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 P0303.
Exact Repair Workflows
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Open the exact repair flow most commonly associated with P0303 on this vehicle.
Open the exact repair flow most commonly associated with P0303 on this vehicle.
Open the exact repair flow most commonly associated with P0303 on this vehicle.
Open the exact repair flow most commonly associated with P0303 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.
Steering wheel shake, brake pedal pulsation, or front-end vibration under braking usually points to rotor, pad, or suspension-related brake issues.
Exact Vehicle Hubs
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Open the exact vehicle hub for a repair workflow commonly associated with P0303.
Open the exact vehicle hub for a repair workflow commonly associated with P0303.
Open the exact vehicle hub for a repair workflow commonly associated with P0303.
Open the exact vehicle hub for a repair workflow commonly associated with P0303.
Open the exact vehicle hub for a repair workflow commonly associated with P0303.
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 2 is misfiring.
Cylinder 4 is misfiring.
Frequently Asked Questions
- Why only cylinder 3?
- If only one cylinder misfires, the cause is specific to that cylinder — its plug, coil, injector, or compression.
- How do coils fail?
- Ignition coils fail from heat cycling, age, and sometimes from running with worn spark plugs that force higher voltage output.
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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