P0303: Falha de Combustão Detetada no Cilindro 3
O código de avaria DTC P0303 indica que o Módulo de Controlo do Motor (ECM/PCM) detetou uma falha de combustão completa ou recorrente isolada especificamente no Cilindro 3. Num motor diesel de rampa comum (common rail) - que prescinde de velas de ignição -, a deteção de falhas é calculada unicamente pelo sensor de posição da cambota (CKP) de alta resolução através da monitorização de variações submicrossegundo na velocidade angular. Quando o tempo de combustão/expansão do Cilindro 3 (30° a 90° Após o Ponto Morto Superior / ATDC) produz uma desaceleração rotacional em vez do pico de aceleração angular calibrado (tipicamente >2.0% dos ciclos monitorizados), o código P0303 é registado.
🚗 Segurança operacional, custos típicos e verificação
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🚦 Segurança de condução e risco mecânico
Avaliação imediata e necessidade de reboqueFalha de Combustão no Cilindro 3 - Condução Permitida Apenas com Baixa Carga de Motor
O cilindro 3 não está a realizar a combustão eficiente do gasóleo. Se a luz de aviso do motor (Check Engine) estiver a piscar, desligue o motor de imediato. Se estiver fixa, conduza moderadamente até uma oficina especializada. Evite acelerações bruscas ou regimes elevados de carga.
RISCOS MECÂNICOS SE CONTINUAR A CONDUZIR:Acumulação de combustível não queimado no coletor de escape, colmatação prematura do filtro de partículas (DPF) e fadiga prematura dos bronzes de biela devido a harmónicas torcionais desequilibradas.Sintomas observáveis no veículo:- Severe engine hesitation, stumbling, and cabin shaking at idle and during acceleration
- Misfire smooths out slightly at higher RPM but vehicle feels completely down on power
- Noticeable grey/black exhaust smoke with stinging unburnt diesel odor
- Automatic transmission reluctant to upshift due to torque calculation mismatch
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💰 Orçamento típico de oficina
Níveis de custo previstos para peças e mão de obraManutenção menor / Filtro30 € - 100 €: Substituição do filtro de combustível, limpeza de contactos do chicote elétrico e teste da vela de incandescência.Limpeza de sensor, troca do filtro de combustível, verificação de fusíveis ou chicote elétrico.
Substituição válvula / Sensor200 € - 450 €: Injetor de rampa comum reconstruído montado com anilha de vedação em cobre nova.Substituição de componente individual (válvula reguladora, unidade dosadora ou injetor remanufaturado).
Reparação maior / Bomba e injetores1000 € - 2300 €+: Injetor novo de origem (Bosch/Denso), tubo de alta pressão da rampa comum e reaprendizagem dos parâmetros de compensação na ECU.Revisão de bomba de alta pressão, jogo de injetores novos ou substituição do conjunto DPF.
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🧰 Verificações visuais rápidas na garagem
Diagnóstico em 5 minutos sem ferramentas antes de chamar o reboque1Verificar o tubo de alta pressão do Cilindro 3: Com o motor frio e desligado, confirme se o tubo metálico e a respetiva abraçadeira amortecedora estão firmes e sem folgas anormais.2Inspecionar a linha de retorno de injetores: Verifique se a ligação rápida em T plástica do retorno do cilindro 3 apresenta fissuras ou vestígios de fuga de gasóleo.3Consultar o histórico de manutenção: Verifique a quilometragem do filtro de combustível - um filtro saturado reduz a pressão dinâmica de alimentação fornecida pela unidade doseadora à rampa. - 04
🛡️ Escudo contra diagnósticos errados na oficina
Perguntas técnicas para evitar substituição desnecessária de peças"Diga: 'Podemos realizar um teste de compressão relativa via equipamento de diagnóstico OBD antes de remover o injetor do cilindro 3?'"
"Diga: 'Por favor, execute um teste de fluxo no retorno de injetores utilizando provetas graduadas durante 3 minutos em ralenti para verificar o caudal de fuga.'"
Nota técnica: Faça estas perguntas ao mecânico antes de aprovar orçamentos elevados:
Triagem de oficina em 30 segundos
- Violent engine shaking, severe vibration, and rhythmic thumping at idle (running distinctly on 3 cylinders)
- Flashing or steady Check Engine Light (MIL) on dashboard, accompanied by flashing glow plug light and ESP/traction warning
- Massive loss of engine power, sluggish throttle response, and inability to accelerate up highway gradients
- Completely failed Cylinder 3 fuel injector (blown solenoid coil, seized command piston, or cracked nozzle needle)
- Low mechanical cylinder compression on Cylinder 3 caused by a burnt exhaust valve, broken rocker arm, or holed piston
- Burned-out or heavily carbon-crusted Cylinder 3 glow plug preventing compression ignition during cold ambient starts
Connect scan tool live telemetry: compare Target Fuel Rail Pressure vs Actual Rail Pressure and log metering valve command PWM duty cycle during idle and road load.
Expensive Diagnostic Pitfall & Technical Reality
P0303 means Cylinder 3 has low mechanical compression requiring an expensive engine rebuild or replacement of all 4 common rail injectors ($1,800 - $3,500).
Diesel engines measure misfires electronically by detecting crankshaft deceleration after Cylinder 3 fires. In over 80% of verified cases, the mechanical cylinder block, piston rings, and valves are in pristine condition. The failure is driven by severe backleak through the Cylinder 3 injector control valve (dropping hydraulic rail pressure below atomization threshold), a burned copper sealing washer at the nozzle tip blowing combustion gas into the engine bay, or an injector solenoid harness connector with loose spring tension.
Unnecessary engine teardown or buying 4 new injectors ($2,200+) vs replacing the $3 copper crush washer or rebuilding the control valve ($120), saving over $2,000.
Motores e plataformas de injeção mais afetados
Este código de falha afeta principalmente as seguintes plataformas diesel common rail. Consulte a família do motor para falhas típicas e números de peças de reposição:
Volkswagen / Audi 2.0 TDI EA189 (Passat, Golf, Tiguan, A4, A6)
Bosch CRI2.2 Solenoid / CRI3 PiezoSintoma típico: Noticeable engine hunting at idle, cold start shiver, and flashing glow plug spiral indicator.
Falha típica de fábrica: Cylinder 3 injector nozzle needle micro-seizing due to carbon varnish, or piezo stack capacitance leakage.
0445110369 / 03L130277B (Bosch Injector)BMW 3.0d M57N / N57 Straight-6 (330d, 530d, 730d, X5)
Bosch CRI3 Piezo Common Rail SystemSintoma típico: Engine shakes under light throttle; Cylinder 3 Smooth Running value exceeds +4.5 mg/stroke in ISTA diagnostics.
Falha típica de fábrica: Piezo actuator crystal moisture penetration and high electrical capacitance leakage on Cylinder 3.
0445115077 / BMW 13537796042 (Piezo Injector)Mercedes-Benz 3.0 CDI V6 OM642 (ML320, E320, GL350, Sprinter)
Bosch Piezo Common Rail CDISintoma típico: Rhythmic chuffing noise from driver-side cylinder bank, loss of power, and P0303 stored.
Falha típica de fábrica: Copper sealing washer on Cylinder 3 burning through, resulting in severe carbon encrustation around the injector body.
A6420701987 / Bosch 0445115064 / A6110170060 (Copper Seal)Ford Transit 2.0 EcoBlue / 2.2 TDCi (Panther & Puma)
Continental / Denso Common RailSintoma típico: Powertrain warning lamp on motorway inclines, engine shudders under heavy load, and P0303 stored.
Falha típica de fábrica: Injector 3 spill valve internal wear dumping fuel pressure; or wiring harness rubbing against cylinder head lifting bracket.
2143478 / Continental A2C9626040080 / 1746967Cylinder Balance & Injector Deviation Guide
Common rail diesel cylinder balance & smooth running diagnostic guide. Balance rates, mg/stroke deviation, P0263 misfire, compression vs injector test.
Circuito de comando e lógica do atuador
1. Dynamic In-Demand Fuel Metering
Diesel compression ignition requires three mandatory physical conditions: high cylinder compression (>22 bar producing air temperatures above 500°C), precise atomization of high-pressure diesel fuel (>250 bar cranking, >1400 bar running), and exact injection timing. The ECM tracks the rotational speed of the flywheel tone ring (60-2 or 36-2). When Cylinder 3 fires correctly, crankshaft rotational speed accelerates sharply. If combustion fails completely (zero heat release), the drag of compressing air causes the crankshaft to slow down rapidly during Cylinder 3's segment, triggering the misfire monitor.
2. Closed-Loop PID Deviation Monitoring
The ECM evaluates misfire data across two independent severity windows: 1. Catalyst / DPF Damaging Window (200 engine revolutions): If the misfire rate is severe enough to allow raw fuel into the exhaust (causing DPF melting), the Check Engine Light flashes violently. 2. Emissions Compliance Window (1,000 engine revolutions): If misfire percentage exceeds 2.0% to 3.0%, a continuous DTC P0303 is logged. The ECM attempts initial compensation by adding fuel via Smooth Running Control (SRC); if the cylinder fails to respond, the ECM cuts fuel to Cylinder 3 to prevent catalytic converter destruction.
3. Diagnostic Trap: Normally Open (NO) vs Normally Closed (NC) Valves
Misfire (P0303) vs Balance Contribution (P0269) Diagnostic Rule: P0269 indicates PARTIAL combustion (the cylinder is running but producing less torque due to coked nozzle holes or minor leakage). P0303 indicates a COMPLETE DEAD MISS: Cylinder 3 has suffered complete combustion failure. In diesel workshops, a dead miss on a single cylinder is caused by one of three primary failures: 1. Complete injector failure (blown solenoid coil, zero fuel injection); 2. Major mechanical compression loss (bent valve, holed piston, broken rocker arm); or 3. Cold-start glow plug burn-out preventing ignition in cold ambient temperatures.
Parâmetros físicos elétricos e hidráulicos
Protocolo de Diagnóstico de Oficina Passo a Passo
Injector Cross-Swap Physical Verification (Hardware vs Mechanics)
Remove the Cylinder 3 fuel injector and swap it with Cylinder 1 (using brand-new annealed copper crush washers). Reprogram the respective IMA/QR calibration codes into the ECM via scan tool. Clear trouble codes and start the engine. If the misfire code moves from P0303 to P0301 (Cylinder 1), the injector has an internal mechanical/hydraulic failure: replace it. If the misfire remains stubbornly on Cylinder 3 (P0303), the problem is 100% mechanical (compression/valvetrain) or wiring.
Electronic Relative Compression & Mechanical Gauge Test
Execute an electronic 'Relative Compression Test' via diagnostic scan tool, which monitors starter current draw and crankshaft angular speed across each cylinder's compression stroke. If Cylinder 3 shows <85% relative compression, remove the Cylinder 3 glow plug and thread in a physical diesel mechanical compression gauge. Crank engine: compression must exceed 22 bar (320 psi) with <3 bar variance to companion cylinders. A reading below 18 bar confirms blown piston rings, burnt valves, or a blown head gasket.
Individual Injector Backleak (Return Flow) Measurement
Disconnect the low-pressure fuel return lines from all injectors. Attach graduated transparent test tubes to the return nipples. Crank the engine for 15 seconds (or run at warm idle for 2 minutes). A healthy injector returns less than 20-25 mL at idle. If Cylinder 3 returns excessive fuel (>40 mL) or fills the bottle instantly during cranking, its internal control valve has collapsed, dumping rail pressure and preventing the needle from lifting.
Injector Solenoid Coil Resistance & 250V Megohmmeter Test
Disconnect the Cylinder 3 injector harness. Using a precision digital multimeter on the 200 Ω scale, measure coil resistance: solenoid injectors must measure 0.20 Ω to 0.45 Ω @ 20°C; piezo injectors must measure 180 kΩ to 220 kΩ. Next, test insulation resistance to the metal body with an automotive insulation tester set to 250V/500V test voltage (must exceed >10 MΩ). A low reading confirms high-voltage dielectric breakdown arcing into the cylinder head.
Glow Plug Resistance & Power Feed Audit (Cold Start Misfires)
If the P0303 misfire occurs exclusively during the first 3 to 5 minutes following a cold start, disconnect the Cylinder 3 glow plug lead. Measure resistance between the glow plug center terminal and engine cylinder block ground. A healthy glow plug measures 0.4 Ω to 1.2 Ω. An open circuit (infinite resistance / OL) confirms a burned-out glow plug that leaves Cylinder 3 too cold to ignite diesel.
Cylinder 3 Valvetrain & Camshaft Lobe Inspection
Remove the engine valve/camshaft cover. Visually inspect the intake and exhaust camshaft lobes and roller rocker arms for Cylinder 3. Look for worn, flattened camshaft lobes (very common on high-mileage VAG TDI and Ford engines) or collapsed hydraulic lash adjusters. A flattened intake cam lobe prevents the intake valves from opening fully, starving the cylinder of oxygen.
Reparo de hardware e lista de peças BOM
Cylinder 3 Fuel Injection & Combustion Sealing Interface
F 00V C17 503 / OEM Copper Crush Washer
Gas-tight sealing ring between injector nozzle shoulder and cylinder head bore seat (prevents combustion blowby)
F 00V C01 359 / F 00R J01 692
Controls hydraulic back-pressure above injector command piston; micro-crack allows fuel bypass
M6 x 88mm Torx T40 Yield Bolt (Engine-specific)
Provides critical clamping load to hold injector against 180+ bar peak cylinder combustion pressure
Calculadora interativa de tolerâncias Common Rail
Componentes de injeção associados
The following genuine OEM fuel pumps and common rail injectors are verified factory equipment for engines reporting fault protocol P0303. Cross-reference operating pressures and tightening torques before sub-assembly replacement:
0445115077BOSCH
BOSCH 0445115077 Piezo Common Rail Injector for BMW 330d / 530d / X5 3.0d M57N2
View Technical Specs & Fitment →0445110369BOSCH
0445110369 Injector: VW 2.0 TDI EA189 CFFB CFHC Specs
View Technical Specs & Fitment →0445115064BOSCH
BOSCH 0445115064 Common Rail Injector for Mercedes-Benz C/E/ML/Sprinter & Jeep Grand Cherokee 3.0 CDI OM642
View Technical Specs & Fitment →095000-5880Denso
095000-5880 Denso Toyota 2KD-FTV Injector: 23670-30050 Data
View Technical Specs & Fitment →28337917Delphi
28337917 Delphi Bobcat D24 Injector: 7030364 Specs & Data
View Technical Specs & Fitment →095000-8340Denso
095000-8340 Denso Mitsubishi 4D56 HP Injector: 1465A367 Data
View Technical Specs & Fitment →Reset de adaptação da bomba e ciclo de aprendizado
Following replacement of the Cylinder 3 fuel injector, glow plug, or cylinder head servicing, execute the adaptation routine:
1. Enter the new 6-to-30 digit alphanumeric calibration code (IMA/QR code) stamped on the top of the new Cylinder 3 injector into the ECM via scan tool.
2. Clear all stored diagnostic trouble codes and confirm engine coolant temperature is above 75°C (167°F).
3. Access scan tool 'Engine Control Module' -> 'Special Functions' -> select 'Reset Cylinder Balance / Smooth Running Values'.
4. Start the engine and allow it to idle undisturbed in park/neutral for 5 minutes without touching any pedals, allowing the ECM to build initial torque offsets.
5. Accelerate vehicle smoothly in 4th gear to 80 km/h (2200 RPM), then release throttle completely to coast down in gear to 35 km/h (minimum 8s overrun).
6. Repeat this acceleration and coast-down sequence 5 times. Return to workshop and confirm Cylinder 3 misfire counter remains at absolute zero.
Diagnóstico diferencial e avarias associadas
Random or Multiple Cylinder Misfire Detected
Multi-cylinder misfire code triggered when systemic issues (air in fuel, bad fuel, low rail pressure) cause misfiring across multiple cylinders.
Cylinder 3 Contribution/Balance Fault
Milder predecessor fault indicating Cylinder 3 is producing degraded torque; if contribution degrades further into complete flameout, P0303 triggers.
Injector Circuit/Open - Cylinder 3
Electrical circuit fault code on Cylinder 3; if an injector wiring open/short develops, P0203 will trigger alongside or override P0303.
Casos reais de oficina
2015 Opel Vivaro 1.6 CDTI (R9M BiTurbo)(174,000 km)
Perguntas técnicas frequentes
O que significa o código de avaria P0303?
O código de avaria DTC P0303 indica que o Módulo de Controlo do Motor (ECM/PCM) detetou uma falha de combustão completa ou recorrente isolada especificamente no Cilindro 3. Num motor diesel de rampa comum (common rail) - que prescinde de velas de ignição -, a deteção de falhas é calculada unicamente pelo sensor de posição da cambota (CKP) de alta resolução através da monitorização de variações submicrossegundo na velocidade angular. Quando o tempo de combustão/expansão do Cilindro 3 (30° a 90° Após o Ponto Morto Superior / ATDC) produz uma desaceleração rotacional em vez do pico de aceleração angular calibrado (tipicamente >2.0% dos ciclos monitorizados), o código P0303 é registado.
Quais são os sintomas mais comuns de P0303?
Violent engine shaking, severe vibration, and rhythmic thumping at idle (running distinctly on 3 cylinders), Flashing or steady Check Engine Light (MIL) on dashboard, accompanied by flashing glow plug light and ESP/traction warning, Massive loss of engine power, sluggish throttle response, and inability to accelerate up highway gradients, Dense clouds of white or blue-grey exhaust smoke on cold start (raw unburned atomized diesel fuel vapor), Overwhelming raw diesel exhaust odor noticeable around the vehicle and through cabin air vents, Scan tool live data shows Cylinder 3 misfire counter incrementing rapidly (>50 counts per 1000 revolutions).
O que causa P0303 em um motor diesel?
Completely failed Cylinder 3 fuel injector (blown solenoid coil, seized command piston, or cracked nozzle needle); Low mechanical cylinder compression on Cylinder 3 caused by a burnt exhaust valve, broken rocker arm, or holed piston; Burned-out or heavily carbon-crusted Cylinder 3 glow plug preventing compression ignition during cold ambient starts; Broken, corroded, or shorted wiring harness wire between the ECM and the Cylinder 3 fuel injector connector; Internal low-side power MOSFET driver transistor failure for Cylinder 3 inside the Engine Control Module (ECM); Intake valve carbon choking or stuck-shut intake swirl flap starving Cylinder 3 of necessary fresh air charge.
É seguro dirigir com o código P0303 ativo?
🟡 Cuidado: Modo de segurança / Visitar oficina
Quanto custa reparar o código de falha P0303?
Os custos típicos de reparação para o código P0303 dependem da causa raiz e do nível de intervenção: Nível 1 (Manutenção ligeira / DIY): 30 € - 100 €: Substituição do filtro de combustível, limpeza de contactos do chicote elétrico e teste da vela de incandescência. (Limpeza de sensor, troca do filtro de combustível, verificação de fusíveis ou chicote elétrico.); Nível 2 (Substituição de componente): 200 € - 450 €: Injetor de rampa comum reconstruído montado com anilha de vedação em cobre nova. (Substituição de componente individual (válvula reguladora, unidade dosadora ou injetor remanufaturado).); Nível 3 (Subconjunto principal): 1000 € - 2300 €+: Injetor novo de origem (Bosch/Denso), tubo de alta pressão da rampa comum e reaprendizagem dos parâmetros de compensação na ECU. (Revisão de bomba de alta pressão, jogo de injetores novos ou substituição do conjunto DPF.). Valores de referência de oficinas. Mais de 70% das ocorrências são resolvidas no Nível 1 ou 2 sem substituição de subconjuntos inteiros.
Can a bad glow plug cause code P0303 in a diesel engine?
Yes, but specifically during cold starts and the first 3 to 5 minutes of engine warm-up. Unlike gasoline spark plugs which fire continuously, diesel glow plugs only operate during pre-glow and post-glow phases to keep cold cylinder walls warm. If the Cylinder 3 glow plug is burned out, cold compression cannot reach the 500°C auto-ignition temperature of diesel, causing Cylinder 3 to misfire (P0303) and puff white unburned fuel smoke until the cylinder block heats up.
Why does my diesel car misfire on Cylinder 3 under heavy load but idle fine?
At idle, common rail fuel pressure is only 250 to 350 bar, and the injector needs to deliver only a tiny 5 mg micro-pulse. Under full load, rail pressure spikes to 1800+ bar and fuel delivery increases tenfold. If the Cylinder 3 injector has internal control valve wear (excessive backleak) or a partially clogged nozzle, it can deliver enough fuel at low pressure to idle smoothly, but completely fails to deliver the massive volume demanded at 1800 bar, dropping cylinder torque and triggering P0303.
What is the fastest way to confirm whether the Cylinder 3 injector is bad?
The most reliable test is the physical cross-swap. Remove the Cylinder 3 injector and swap it with Cylinder 1 (always install new annealed copper seating washers). Enter the calibration codes into the scan tool and drive the vehicle. If the misfire moves to Cylinder 1 (P0301), you have 100% proven the injector is defective. If the misfire stays on Cylinder 3 (P0303), you know the injector is innocent and must check mechanical cylinder compression.