PROTOCOLO DE OFICINA DIESEL OBD-II8-10 min read
P0269Falhas de Ignição e EquilíbrioGravidade Alta💡 Luz de injeção acesa

P0269: Falha de Contribuição / Equilíbrio do Cilindro 3

O código de diagnóstico de avaria (DTC) P0269 indica que o Módulo de Controlo do Motor (ECM/PCM) detetou que o cilindro 3 não está a gerar o impulso de binário mecânico esperado na cambota, provocando um desequilíbrio rotacional entre cilindros. Nos motores diesel de rampa comum (common rail), o ECM calcula continuamente o trabalho de cada cilindro através da medição de variações na escala dos submicossegundos na aceleração angular da cambota, lidas pelo sensor de posição da cambota (CKP) durante o tempo de combustão/expansão entre 30° - 90° Após o Ponto Morto Superior (APMS / ATDC). Se o algoritmo de Controlo de Funcionamento Suave (SRC) / Calibração de Débito Nulo (ZFC) do ECM tiver de aplicar uma compensação de débito de combustível excessiva (tipicamente > +3.0 a +4.5 mg/ciclo) para estabilizar a marcha-lenta, ou se o rendimento do cilindro descer 15% - 25% abaixo da média do motor, o código P0269 é registado.

🚗 PROTOCOLO DO CONDUTOR & REPARAÇÃO

🚗 Segurança operacional, custos típicos e verificação

🟡 Cuidado: Modo de segurança / Visitar oficina
  1. 01

    🚦 Segurança de condução e risco mecânico

    Avaliação imediata e necessidade de reboque

    Falha de Contribuição / Equilíbrio do Cilindro 3 - Défice de Contribuição de Binário

    A ECU detetou que o cilindro 3 não está a produzir momento angular suficiente. O débito de injeção caiu ou o refluxo excessivo está a privar a câmara de combustão do volume de gasóleo necessário.

    RISCOS MECÂNICOS SE CONTINUAR A CONDUZIR:Combustível não queimado contínuo ou falhas de combustão por mistura pobre podem provocar sobreaquecimento do catalisador ou acumulação excessiva de fuligem no DPF.
  2. 02

    💰 Orçamento típico de oficina

    Níveis de custo previstos para peças e mão de obra
    Manutenção menor / Filtro40 € - 110 € (Limpeza química do sistema de combustível e substituição do filtro)

    Limpeza de sensor, troca do filtro de combustível, verificação de fusíveis ou chicote elétrico.

    Substituição válvula / Sensor180 € - 480 € (Substituição do injetor do cilindro 3 por peça genuína)

    Substituição de componente individual (válvula reguladora, unidade dosadora ou injetor remanufaturado).

    Reparação maior / Bomba e injetores850 € - 2.200 € (Revisão da compressão mecânica do motor ou intervenção na cabeça do motor)

    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.

  3. 03

    🧰 Verificações visuais rápidas na garagem

    Diagnóstico em 5 minutos sem ferramentas antes de chamar o reboque
    11. Verificar a correção de débito dos injetores em tempo real: desvio superior a +3.0 mg/str indica bocal obstruído ou refluxo excessivo.
    22. Inspecionar o assento do injetor do cilindro 3 quanto a borbulhamento de gasóleo ou acumulação de resíduos carbonosos tipo alcatrão.
    33. Trocar o injetor do cilindro 3 com o do cilindro 1; se o código de avaria migrar para P0263, fica comprovado o defeito no injetor.
  4. 04

    🛡️ Escudo contra diagnósticos errados na oficina

    Perguntas técnicas para evitar substituição desnecessária de peças
    ""Apresente os relatórios de dados do equilíbrio dos cilindros antes e depois da limpeza química antes de prescrever a substituição do injetor.""
    ""Confirme se a compressão mecânica no cilindro 3 está dentro de uma tolerância de 10% em relação aos cilindros adjacentes.""
    ""Assegure-se de que a sede do novo injetor é fresada com ferramenta adequada se a passagem de gases de combustão tiver erodido a superfície da cabeça do motor.""

    Nota técnica: Faça estas perguntas ao mecânico antes de aprovar orçamentos elevados:

🔧 PROTOCOLO TÉCNICO PROFISSIONAL & OFICINARAPID ASSESSMENT

Triagem de oficina em 30 segundos

Sintomas principais
  • Noticeable engine shudder, rough idle, and cabin vibration during warm idle (especially in Drive at traffic lights)
  • Hesitation, flat spots, or rhythmic surging during light-to-moderate throttle cruising at 1200 to 2000 RPM
  • Check Engine Light (MIL) illuminated, occasionally accompanied by flashing glow plug light or traction control warning
Principais causas prováveis
  • Partially clogged, carbon-coked, or eroded spray holes in the Cylinder 3 fuel injector nozzle tip
  • Excessive internal control valve wear (backleak) in Cylinder 3 injector, reducing effective injection pressure and fuel delivery
  • Incorrect, corrupted, or uncalibrated IMA / QR injector calibration code programmed into the ECM for Cylinder 3
Primeira ação necessária

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

❌ Erro comum na oficina:

P0269 means Cylinder 3 has low mechanical compression requiring engine teardown or full injector set replacement ($3,000 - $5,500).

🔍 Realidade técnica e hidráulica:

P0269 is an electronic cylinder balancing limit code (Smooth Running Control). The ECM measures crankshaft micro-acceleration after Cylinder 3 fires and adjusts fuel trim (mg/stroke) to keep engine idle smooth. If the required trim exceeds calibrated limits (typically >±4.5 mg/stroke), P0269 is flagged. In over 80% of verified cases, mechanical compression is normal. The root cause is an incorrectly typed or missing IMA/IQA injector code in the ECM, a partially clogged injector nozzle spray hole, or excessive control valve backleak.

💡 Protocolo de verificação técnica:

Unnecessary engine teardown ($3,500+) vs verifying and reprogramming the 7-to-20-character IMA injector code into the ECM ($0 - $50) or rebuilding the injector ($120), saving thousands.

Severe Piston Crown Thermal Erosion & Bore Washing Hazard

CRITICAL WORKSHOP WARNING: Never ignore a Cylinder 3 contribution fault code P0269! In diesel combustion, if the balance fault is caused by a worn or carbon-fouled injector nozzle needle that is dripping or failing to atomize fuel into a fine 10-micron mist, raw liquid diesel sprays directly against the aluminum piston bowl.

MANDATORY PROTOCOL: Under highway load, this creates an intense localized torching fire that melts the piston crown (holed piston) or washes oil film off the cylinder wall, causing catastrophic cylinder bore scoring and crankcase blow-by. If the engine emits black smoke under throttle or if the oil dipstick level is rising with diesel smell, discontinue driving immediately and perform an injector backleak and flow test.

PLATFORM ARCHITECTURE

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:

Mercedes-Benz 2.1 CDI (OM651 / OM646)

Delphi CRD2 / Bosch Common Rail Injection

Falha típica de fábrica: Delphi piezo to solenoid conversion wiring harness chafing, differential pressure sensor internal diaphragm drift.

Componente-chave:A6510704987, A6510700587, A0061539528

Ford 6.7L Powerstroke V8 Diesel

Bosch CP4.2 High-Pressure Common Rail System

Falha típica de fábrica: EGR cooler carbon clogging, DEF injector white crust crystallization, fuel volume control valve harness chafing.

Componente-chave:BC3Z-9A543-A, FC3Z-9F593-B, BC3Z-5J281-A

Volkswagen / Audi 2.0 TDI (EA189 / CFFB / CFGB)

Bosch EDC17 Common Rail System

Falha típica de fábrica: Piezo stack degradation, injector harness terminal fretting, DPF differential pressure sensor silicone tube split.

Componente-chave:03L130277, 0445110369, 076906051A

BMW 2.0d / 3.0d (N47 / N57 / M57TU2)

Bosch CRI2.5 / CRI3.0 Common Rail

Falha típica de fábrica: Injector balance drift beyond +/- 4.0 mg/stroke, glow plug control unit (BERU) power lead failure, DPF backpressure accumulation.

Componente-chave:13537805428, 0445116024, 12217801201
WORKSHOP MASTER TEARDOWN GUIDE

Cylinder Balance & Injector Deviation Guide

Common rail diesel cylinder balance & smooth running diagnostic guide. Balance rates, mg/stroke deviation, P0263 misfire, compression vs injector test.

Read Full Master Guide →
THEORY OF OPERATION

Circuito de comando e lógica do atuador

1. Dynamic In-Demand Fuel Metering

Modern common rail diesel engines operate without a physical distributor or mechanical governor; cylinder-to-cylinder torque equalization is performed purely through software. The ECM monitors flywheel tooth passage times using a high-precision magnetic or Hall-effect CKP sensor reading a 60-2 or 36-2 target wheel. If Cylinder 3 produces less power due to a partially coked injector nozzle, excessive internal hydraulic backleak, or slightly degraded mechanical compression, the crankshaft slows down momentarily during Cylinder 3's power segment. The ECM immediately compensates by extending the injection duration for Cylinder 3.

2. Closed-Loop PID Deviation Monitoring

The Smooth Running Control (SRC) algorithm calculates a real-time fuel trim offset for each cylinder (displayed in scan tools as 'Cylinder Balance Rate' or 'Injector Quantity Offset', typically scaled in mg/stroke or mm³/stroke). A healthy cylinder operates between -1.5 mg/stroke and +1.5 mg/stroke. When Cylinder 3's required fuel correction exceeds calibrated upper limits (+3.5 to +6.0 mg/stroke) for longer than 500 consecutive combustion cycles at warm idle, or during an automated cylinder cutout diagnostic sweep, the ECM flags P0269 and locks the balance rate into freeze frame memory.

3. Diagnostic Trap: Normally Open (NO) vs Normally Closed (NC) Valves

Contribution Fault (P0269) vs Misfire (P0303) Diagnostic Distinction: Technicians frequently confuse these two codes. P0303 indicates a COMPLETE combustion failure (misfire/dead miss, zero flame propagation), usually caused by an electrical open circuit, completely blocked injector, or zero compression. In contrast, P0269 indicates PARTIAL combustion: fuel is injecting and igniting, but the kinetic energy delivered is suboptimal compared to companion cylinders. In over 75% of diesel cases, P0269 is caused by mechanical injector nozzle varnish or excessive control valve return leakage, NOT electrical circuit failure.

ENGINEERING SPECIFICATIONS

Parâmetros físicos elétricos e hidráulicos

Solenoid Coil DC ResistanceCommon Rail Solenoid Injector: 0.20 - 0.45 Ω @ 20°C; Piezo Injector: 180 kΩ - 220 kΩ (Capacitance: 2.5 - 3.5 µF)Measured @ 20°C across terminals 1 & 2
Insulation Resistance> 10 MΩ measured between injector electrical pins and cylinder head metal chassis (ground)Between terminals and pump body (ground)
Operating Supply Voltage80 V - 90 V DC peak boost voltage (Solenoid) or 140 V - 200 V DC (Piezo); Battery supply to ECM: > 12.0 VHigh-side feed from ECM / main relay
PWM Frequency StandardMulti-pulse high-speed current waveform; Peak pull-in current: 20 A - 30 A; Hold current: 10 A - 12 ASquare-wave PWM modulation
Idle Duty Cycle (Warm Engine)Cylinder 3 Balance Fuel Trim (SRC): Normal is -1.5 to +1.5 mg/stroke; Fault threshold > +3.0 to +4.5 mg/strokeNominal baseline at 250–350 bar
Full-Load Duty Cycle (WOT)Dynamic Backleak Flow Limit: < 25 mL/min per injector @ warm idle; < 5 mL total per cylinder during 15s starter crankingMaximum high-speed fuel delivery demand
Low-Pressure Feed SupplyMechanical Cylinder Compression: 22.0 to 32.0 bar (320-465 psi); Maximum allowable variance to other cylinders < 3.0 bar (< 10%)Measured at pump fuel inlet
Internal Cascade BackpressureCylinder Cutout RPM Drop: Must produce a 45 to 65 RPM drop when Cylinder 3 is disabled via scan toolControlled by overflow cascade valve
PROCEDURAL PROTOCOL

Protocolo de Diagnóstico de Oficina Passo a Passo

STEP 1

Live Scan Tool Cylinder Balance Rate (SRC) Logging

Warm the engine until coolant temperature exceeds 80°C (176°F). Access scan tool live data for 'Cylinder Balancing / Smooth Running Control'. Observe the real-time fuel trim for all cylinders at stable idle (A/C off, transmission in park/neutral). Normal values are -1.5 to +1.5 mg/stroke. If Cylinder 3 reads +3.5 to +5.5 mg/stroke, the ECM is struggling to add massive fuel to compensate for a weak Cylinder 3 power stroke.

STEP 2

Automated Cylinder Cutout RPM Drop Test

Using scan tool bi-directional controls, perform an automated 'Cylinder Cutout Test'. The ECM will disable fuel injection to each cylinder sequentially. On a healthy cylinder, shutting off injection causes a sharp 45 to 65 RPM drop and noticeable engine stumble. If cutting out Cylinder 3 produces less than a 20 RPM drop, it proves Cylinder 3 was barely contributing power before being cut.

STEP 3

Individual Injector Backleak (Return Flow) Measurement

Disconnect the low-pressure fuel return line from all injectors. Attach graduated transparent test tubes to the return nipples. Start the engine and run at warm idle for exactly 2 minutes. Measure return volume in milliliters. A healthy injector returns less than 20-25 mL. If Cylinder 3 returns >40 mL, its internal hydraulic control valve seat is eroded, dumping rail pressure into the return.

STEP 4

Electronic Relative Compression & Mechanical Gauge Test

Execute an electronic 'Relative Compression Test' via scan tool, which monitors starter current draw across each compression stroke. All cylinders must match within 95% to 100%. If Cylinder 3 shows <85%, remove the glow plug and perform a physical mechanical compression gauge test (must exceed 22 bar with <3 bar variance). Low compression confirms a valve, ring, or head gasket issue.

STEP 5

Injector Cross-Swap Physical Verification

To conclusively isolate the injector from engine mechanics, remove the Cylinder 3 injector and swap it with Cylinder 1 (using new copper washers). Reprogram the respective IMA/QR codes into the ECM. Clear DTCs and road-test the vehicle. If the fault moves from P0269 to P0263 (Cylinder 1), the injector is 100% defective. If the fault stays on P0269 on Cylinder 3, the cause is mechanical compression or valvetrain wear.

STEP 6

IMA / QR Calibration Code Verification

Read the physical 6-to-30 digit alphanumeric code laser-etched onto the top plastic head of the Cylinder 3 injector. Compare this code against the code stored in the ECM memory using your scan tool. If an uncalibrated replacement injector was installed without programming, the ECM uses generic default pulse widths that can cause a 15% to 20% fueling error, triggering P0269.

COMPONENT-LEVEL REPAIR

Reparo de hardware e lista de peças BOM

Cylinder 3 Fuel Metering Calibration & IMA Coding Architecture

Bosch CRI2 / CRI3 Solenoid Injector Assembly - Cylinder 3

0 445 110 369 / 0 445 116 059

High-precision electro-hydraulic fuel injector with laser-etched IMA calibration classification code

OEM: Protocol: Replace or recalibrate if backleak exceeds 35 mL/min or balance offset remains pegged at >±4.5 mg/stroke after coding
Heat-Treated Annealed Copper Injector Sealing Washer (1.5mm - 2.0mm)

F 00V C17 503 / OEM Copper Crush Washer

Gas-tight sealing ring preventing combustion gas leakage that drops effective cylinder compression

OEM: Protocol: Mandatory replacement whenever injector is removed
Injector Nozzle Micro-Orifice Tip Assembly (7-Hole)

DLLA 150 P 1828 / OEM Nozzle Assembly

Atomizes high-pressure diesel into micro-droplets; clogged micro-holes reduce cylinder contribution

OEM: Protocol: Replace if spray pattern testing shows distorted cone or missing spray plume
Workshop Technical & Economic Benchmark: Injector clamp stretch bolt: 7 Nm + 90° angle turn; Diagnostic scan tool capable of writing IMA/IQA 7-20 digit calibration strings; High-pressure fuel line torque: 28 - 32 Nm.
LIVE WORKSHOP TOOL

Calculadora interativa de tolerâncias Common Rail

IMA / IQA Injector Calibration Code & Checksum Validator

Validate the 7-to-20 character IMA string etched on the injector head. An incorrect character or wrong checksum causes the ECM to reject the code or default to an incorrect fuel trim curve, triggering P0269 contribution faults.

📐 Factory Engineering Tolerance: Allowable Smooth Running Trim: -1.5 to +1.5 mg/stroke
OEM REPLACEMENTS

Componentes de injeção associados

The following genuine OEM fuel pumps and common rail injectors are verified factory equipment for engines reporting fault protocol P0269. Cross-reference operating pressures and tightening torques before sub-assembly replacement:

Common Rail Injector

0445110369BOSCH

0445110369 Injector: VW 2.0 TDI EA189 CFFB CFHC Specs

View Technical Specs & Fitment →
Common Rail Injector

0445116024BOSCH

BOSCH 0445116024 Common Rail Piezo Injector for BMW N47 2.0d & N57 3.0d

View Technical Specs & Fitment →
Common Rail Injector

095000-5880Denso

095000-5880 Denso Toyota 2KD-FTV Injector: 23670-30050 Data

View Technical Specs & Fitment →
Common Rail Injector

28337917Delphi

28337917 Delphi Bobcat D24 Injector: 7030364 Specs & Data

View Technical Specs & Fitment →
Common Rail Injector

095000-8340Denso

095000-8340 Denso Mitsubishi 4D56 HP Injector: 1465A367 Data

View Technical Specs & Fitment →
Common Rail Injector

0445120289Bosch

0445120289 Bosch Perkins 1104D Injector: 2645A749 Data

View Technical Specs & Fitment →
CALIBRATION RELEARN

Reset de adaptação da bomba e ciclo de aprendizado

Following replacement of the Cylinder 3 fuel injector, nozzle servicing, or valve adjustment, execute the adaptation routine:

1. Enter the new alphanumeric calibration code (IMA/QR code) stamped on the new Cylinder 3 injector into the ECM via scan tool.

2. Clear all stored 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 balance rate is within ±1.5 mg/stroke.

DIFFERENTIAL DIAGNOSIS

Diagnóstico diferencial e avarias associadas

P0303

Cylinder 3 Misfire Detected

Hard misfire code indicating complete lack of combustion on Cylinder 3, whereas P0269 indicates combustion occurs but with degraded power delivery.

P0203

Injector Circuit/Open - Cylinder 3

Electrical circuit fault code on Cylinder 3; if an injector wiring fault develops, P0203 will trigger alongside or override P0269.

P0263

Cylinder 1 Contribution/Balance Fault

Companion code on Cylinder 1; swapping injectors between Cylinders 3 and 1 allows immediate isolation of injector hardware vs cylinder mechanics.

FIELD REPAIR REPORTS

Casos reais de oficina

CASE #1

2015 Ford Transit Custom 2.2 TDCi (Puma)(182,000 km)

Reported Complaint:Cold idle shake with mild combustion knock; DTC P0269 stored; Cylinder 3 balance trim pegged at +4.6 mg/stroke.
Teardown Root Cause:Dynamic backleak test: Cylinder 3 returned 62 mL in 2 minutes (Cylinders 1, 2, 4 returned 18-20 mL), confirming internal hydraulic valve erosion.
Repair Solution:Replaced internal control valve assembly on Cylinder 3 injector, generated new 16-character IMA code on test bench, and programmed into ECM. Cylinder 3 balance trim dropped to -0.1 mg/stroke with vibration eliminated.
DIAGNOSTIC FAQ

Perguntas técnicas frequentes

O que significa o código de avaria P0269?

O código de diagnóstico de avaria (DTC) P0269 indica que o Módulo de Controlo do Motor (ECM/PCM) detetou que o cilindro 3 não está a gerar o impulso de binário mecânico esperado na cambota, provocando um desequilíbrio rotacional entre cilindros. Nos motores diesel de rampa comum (common rail), o ECM calcula continuamente o trabalho de cada cilindro através da medição de variações na escala dos submicossegundos na aceleração angular da cambota, lidas pelo sensor de posição da cambota (CKP) durante o tempo de combustão/expansão entre 30° - 90° Após o Ponto Morto Superior (APMS / ATDC). Se o algoritmo de Controlo de Funcionamento Suave (SRC) / Calibração de Débito Nulo (ZFC) do ECM tiver de aplicar uma compensação de débito de combustível excessiva (tipicamente > +3.0 a +4.5 mg/ciclo) para estabilizar a marcha-lenta, ou se o rendimento do cilindro descer 15% - 25% abaixo da média do motor, o código P0269 é registado.

Quais são os sintomas mais comuns de P0269?

Noticeable engine shudder, rough idle, and cabin vibration during warm idle (especially in Drive at traffic lights), Hesitation, flat spots, or rhythmic surging during light-to-moderate throttle cruising at 1200 to 2000 RPM, Check Engine Light (MIL) illuminated, occasionally accompanied by flashing glow plug light or traction control warning, Heavy puffing of grey or black exhaust smoke on sudden acceleration due to unburned fuel in Cylinder 3, Elevated fuel consumption and rough engine shutdown (excessive diesel shudder when turning off the ignition), Scan tool live data displays Cylinder 3 balance rate pegged at high positive compensation (+3.5 to +5.5 mg/stroke).

O que causa P0269 em um motor diesel?

Partially clogged, carbon-coked, or eroded spray holes in the Cylinder 3 fuel injector nozzle tip; Excessive internal control valve wear (backleak) in Cylinder 3 injector, reducing effective injection pressure and fuel delivery; Incorrect, corrupted, or uncalibrated IMA / QR injector calibration code programmed into the ECM for Cylinder 3; Low mechanical cylinder compression on Cylinder 3 caused by worn piston rings, valve seat recession, or blown head gasket; Cylinder 3 glow plug tip coated in thick carbon or burned out, impairing post-start combustion stability in cold engines; Worn camshaft lobe or collapsed hydraulic lifter reducing intake valve lift and starving Cylinder 3 of fresh air charge.

É seguro dirigir com o código P0269 ativo?

🟡 Cuidado: Modo de segurança / Visitar oficina

Quanto custa reparar o código de falha P0269?

Os custos típicos de reparação para o código P0269 dependem da causa raiz e do nível de intervenção: Nível 1 (Manutenção ligeira / DIY): 40 € - 110 € (Limpeza química do sistema de combustível e substituição do filtro) (Limpeza de sensor, troca do filtro de combustível, verificação de fusíveis ou chicote elétrico.); Nível 2 (Substituição de componente): 180 € - 480 € (Substituição do injetor do cilindro 3 por peça genuína) (Substituição de componente individual (válvula reguladora, unidade dosadora ou injetor remanufaturado).); Nível 3 (Subconjunto principal): 850 € - 2.200 € (Revisão da compressão mecânica do motor ou intervenção na cabeça do motor) (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 fuel additive or injector cleaner fix trouble code P0269?

In mild, early-stage cases where P0269 is caused by soft gummy diesel varnish or light carbon deposits on the injector nozzle spray holes, a professional-grade polyetheramine (PEA) or cetane-boosting diesel injector cleaner run through a concentrated dose can dissolve deposits and restore balance rates within 50 to 100 miles. However, if the cause is mechanical control valve erosion (excessive backleak) or low mechanical cylinder compression, chemical additives will have zero effect and the injector must be replaced.

Why does the scan tool show positive fuel trim (+4.0 mg/stroke) for a weak cylinder?

In common rail diesel ECM software, the cylinder balance trim represents COMPENSATION. If Cylinder 3 is weak (delivering less power than the other cylinders), the engine idle would shake and slow down. To prevent this, the ECM's Smooth Running Control algorithm adds EXTRA fuel (positive trim, such as +4.0 mg/stroke) to Cylinder 3 to prop up its power stroke and match the other cylinders. A high positive number means the cylinder is weak.

Is trouble code P0269 safe to drive with?

You can drive short distances to reach a repair facility, but prolonged driving is not recommended. If the contribution fault is caused by an injector nozzle with a bad spray pattern (dripping rather than atomizing), liquid diesel will pool on the piston crown, risking severe piston melting and engine failure under highway loads. Furthermore, incomplete combustion creates high soot levels that will rapidly clog your DPF filter.