System: Powertrain (P-Code)
SAE Standard (Generic)
Family: Misfire Single Cylinder
Code P0303: Cylinder 3 Misfire Detected
Diagnostic & Technical Explanation
Code P0303 (Cylinder 3 Misfire Detected) sets when the ECM's misfire monitor isolates repeated combustion events lost on one specific cylinder (or, for the unspecified variant, a single cylinder it cannot pin down). The diagnosis path is identical regardless of which cylinder number is reported: the fault lives in that cylinder's ignition, fuel delivery, or mechanical sealing, most commonly a fouled spark plug or failing coil, a clogged or leaking injector, or low compression from a burnt valve or worn rings.
First-listed procedure
Rank #1
Swap spark plug and ignition coil to confirm the cylinder
Easy DIY
This is the first procedure in the authored
consideration order, not a measured cause likelihood. Execute it only when its prerequisites
and diagnostic findings support it. Its cost and labor estimates (where known), the step-by-step procedure and the
remaining 3 procedure(s) are in the licensed dataset. Ordering context.
Full family: Misfire Single Cylinder
What this page does not show
This page publishes the fault mechanism and the code index. The licensed dataset adds, for
every one of the 15,886 codes, the full authored repair set (56,729 procedures in total)
with the fields deliberately withheld here:
- Procedures 2..n after the first-listed procedure
- Aftermarket parts cost ranges in USD (
est_parts_cost_min/max_usd)
- Professional labor-hour estimates (
est_labor_hours)
- Step-by-step diagnostic and repair instructions
- Replacement-part mappings and catalog lookups
- 6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)