P0303 on Mazda
Cylinder 3 Misfire Detected
P0303 on Mazda vehicles indicates cylinder 3 misfire detected. Au7o has documented this code across 7 Mazda models — most commonly on CX-3, CX-5, Mazda3. This code means your engine's computer detected a misfire specifically in cylinder number 3 — that cylinder isn't burning its fuel-air mixture properly or completely. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder is supposed to fire. A misfire wastes fuel, can cause a noticeable shake, rough idle or loss of power, and can flood raw fuel into the exhaust where it may overheat and damage the catalytic converter. Because the fault is isolated to one cylinder, the cause is usually something specific to that cylinder's ignition, fuel delivery, or compression. Typical repair costs on Mazda range from $50 to $5,000, depending on the specific model and root cause.
Common Causes of P0303
- •Worn or fouled spark plug in cylinder 3
- •Failed or weak ignition coil on cylinder 3
- •Bad spark plug wire or boot (where applicable)
- •Clogged or leaking fuel injector for cylinder 3
- •Vacuum or intake air leak affecting that cylinder
- •Low compression (worn rings, burnt/leaking valve, head gasket)
- •Wiring or connector fault at the coil or injector
P0303 on Mazda by Model
Mazda CX-3(1 issue)
- Skyactiv 2.0L Intake Valve Carbon Buildup2016-2021
The 2016-2021 Mazda CX-3 with the 2.0L Skyactiv-G direct injection engine develops carbon deposits on the intake valves over time. Because direct injection sprays fuel directly into the combustion chamber rather than over the intake valves, there is no fuel wash to clean the valve backsides. Oil vapors from the PCV (Positive Crankcase Ventilation) system coat the intake valves and bake into hard carbon deposits. This gradually restricts airflow, causing misfires on cold starts, loss of low-end power, and reduced fuel efficiency. Using conventional oils with high volatility worsens the problem by producing more PCV vapors.
Mazda CX-5(1 issue)
- Carbon Buildup on Intake Valves (Skyactiv)2013-2023
Direct-injection Skyactiv engines accumulate carbon deposits on intake valves due to oil vapors from the PCV system. Without port injection to clean valves, carbon can fuse to valve surfaces over time, typically appearing around 65,000+ miles.
Mazda Mazda3(1 issue)
- 2012-2013 Mazda3 SKYACTIV Cold-Start Misfire from Intake-Valve Deposits2012-2013
Mazda bulletin 01-020/15 covers some 2012-2013 Mazda3 vehicles with SKYACTIV whose check-engine light stores P0300, P0301, P0302, P0303, or P0304 during accelerated warm-up. Mazda says carbon may be deposited around the intake valves and destabilise combustion under a specific cold-start freeze-frame pattern: high calculated load, coolant below 100 degrees Fahrenheit, engine speed above 1,300 rpm, vehicle stopped, specified ignition timing, and less than 45 seconds of run time. The bulletin does not establish routine intake-valve cleaning for every 2012-2025 Mazda3.
Mazda Mazda6(1 issue)
- SkyActiv-G Intake Valve Carbon Buildup (Direct Injection)2014-2021
Because the SkyActiv-G direct-injection engine sprays fuel directly into the cylinder, no detergent fuel ever washes the back of the intake valves. Oil vapor drawn through the PCV system bakes onto the hot valve stems and accumulates as hard carbon, typically becoming noticeable on the 2.5L between 60,000 and 100,000 miles. The deposits restrict airflow and cause rough idle and cold-start misfires that are otherwise hard to diagnose.
Mazda MX-5 Miata(1 issue)
- Crankshaft Position Sensor Failure (NB)1999-2005
The NB Miata (1999-2005) crankshaft position sensor (CPS) is a known failure point. The sensor deteriorates from engine heat, causing intermittent stalling, no-start conditions, and random misfires. Failure is often heat-related - the car runs fine when cold but stalls or dies after reaching operating temperature.
Mazda RX-8(2 issues)
- Apex Seal Failure / Compression Loss2004-2012
The Renesis rotary engine in the RX-8 is infamous for apex seal wear and failure, leading to catastrophic compression loss. Apex seals maintain the combustion chamber seal between the rotor and housing. Heat, carbon deposits, and inadequate lubrication cause seals to wear, chip, or break. Compression testing below 6.5 kg/cm2 indicates rebuild is needed. This is the single most common and feared RX-8 issue.
- Ignition Coil and Spark Plug Rapid Wear Causing Misfires2004-2011
The Renesis rotary uses a coil-near-plug ignition (grouped coils feeding plug wires) with two spark plugs per rotor (leading and trailing) that fire every engine revolution rather than every other one, so coils and plugs wear far faster than on a piston engine. Weak factory coils commonly degrade around 30,000 miles, producing misfires, rough idle, hesitation and power loss. Because unburned fuel then dumps into the catalytic converter, ignoring failing coils accelerates cat clogging.
Mazda Tribute(1 issue)
- Ignition Coil Failure and Misfires2001-2011
Ignition coil-on-plug coils fail causing misfires. Ford 3.0L Duratec V6 coils are prone to cracking and arcing. Usually fails one at a time.
Looking for P0303 on a different make?
View P0303 across all makes →Frequently Asked Questions
What does P0303 mean on Mazda?▼
P0303 stands for "Cylinder 3 Misfire Detected." This code means your engine's computer detected a misfire specifically in cylinder number 3 — that cylinder isn't burning its fuel-air mixture properly or completely. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder is supposed to fire. A misfire wastes fuel, can cause a noticeable shake, rough idle or loss of power, and can flood raw fuel into the exhaust where it may overheat and damage the catalytic converter. Because the fault is isolated to one cylinder, the cause is usually something specific to that cylinder's ignition, fuel delivery, or compression. On Mazda specifically, this code is documented across 7 models.
What causes P0303 on Mazda vehicles?▼
Common causes on Mazda: Worn or fouled spark plug in cylinder 3, Failed or weak ignition coil on cylinder 3, Bad spark plug wire or boot (where applicable), Clogged or leaking fuel injector for cylinder 3, Vacuum or intake air leak affecting that cylinder. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0303 on a Mazda?▼
Repair costs on Mazda range from $50 to $5,000, depending on the specific model and root cause.
Which Mazda models have P0303 documented?▼
Au7o has documented P0303 on 7 Mazda models: CX-3, CX-5, Mazda3, Mazda6, MX-5 Miata, RX-8, Tribute.