P0303
High SeverityCylinder 3 Misfire Detected
Ignition System
What Does P0303 Mean?
Cylinder 3 is misfiring.
Common Fix
Replace spark plug or coil
Estimated Cost (DIY)
$20 - $500
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 Diagnostic Flowchart
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Related Resources
Repair guides, symptom pages, and wiring diagrams related to P0303.
OEM Manual Evidence
Browse →A L L Diagnostic Trouble Codes ( DTC ) — 2013 GMC Truck Yukon XL Denali AWD V8-6.2L Service Manual | Operation CHARM Operation CHARM : Car...
A L L Diagnostic Trouble Codes ( DTC ) — 2013 GMC Truck Yukon XL Denali 2WD V8-6.2L Service Manual | Operation CHARM Operation CHARM : Car...
A L L Diagnostic Trouble Codes ( DTC ) — 2013 GMC Truck Yukon XL 4WD V8-6.0L Service Manual | Operation CHARM Operation CHARM : Car repair...
A L L Diagnostic Trouble Codes ( DTC ) — 2013 GMC Truck Yukon XL 4WD V8-5.3L Service Manual | Operation CHARM Operation CHARM : Car repair...
Exact Repair Workflows
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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
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Open the exact vehicle hub grounded by OEM manual evidence related to P0303.
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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.
Related Repair Guides
If your vehicle has triggered P0303, these DIY repair guides may help: