P03CF

What it means

P03CF means the engine control unit has found that the combustion pressure in cylinder 6 is varying too much, either from one firing cycle to the next or compared with the other cylinders. This is only monitored on engines fitted with in-cylinder pressure measurement, and the exact method and limits depend on the engine. It points to unstable combustion, a mechanical fault in that cylinder, or a fault in the pressure sensing circuit.

Symptoms

• Engine warning light on
• Rough running or uneven idle
• Hesitation or reduced power under load
• Increased fuel consumption
• Misfire codes stored alongside P03CF
• Increased exhaust smoke or a fuel smell

Possible causes

• Faulty or worn injector on cylinder 6 giving an uneven fuel quantity or spray patternlikely
• Ignition fault on cylinder 6 such as a weak coil or worn spark plug (petrol engines)likely
• Cylinder pressure sensor fault, or damaged wiring or connector in its circuitlikely
• Poor compression in cylinder 6 from valve, piston ring, head gasket or valve seat wearpossible
• Carbon build-up or an intake leak affecting cylinder 6 airflow or mixturepossible
• Poor quality or contaminated fuel causing erratic combustionpossible
• Outdated control unit software where a known calibration issue exists for the enginerare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data (load, speed, temperature) for when the fault set.
2. Check for related codes such as misfires, injector circuit faults or sensor supply faults, and deal with those first.
3. Inspect the wiring and connector for the cylinder 6 pressure sensor and injector for damage, corrosion, chafing or water ingress.
4. Check the spark plug and coil on cylinder 6 (petrol), or injector condition and balance rates (diesel), against the other cylinders.
5. View live data for cylinder 6 pressure and compare it with the other cylinders at idle and under load.
6. Look for intake leaks, a dirty intake tract and carbon deposits, and check fuel quality and recent refuelling history.
7. Carry out a compression or leak-down test on cylinder 6 if combustion faults are ruled out.
8. Check for a manufacturer software update or technical bulletin relating to this code on the specific engine.

How to fix

• Repair or replace damaged wiring, connectors or the cylinder 6 pressure sensor once the fault is confirmed.
• Replace the faulty injector or ignition components on cylinder 6.
• Clean carbon deposits and repair any intake leaks found.
• Repair the mechanical fault in cylinder 6, such as valves, rings or head gasket, if the compression test fails.
• Drain and replace contaminated fuel and replace the fuel filter where fitted.
• Update the control unit software only if a known calibration fault applies to that engine.

Can I keep driving?

Nearby codes

• P03CEGenericCylinder 6 Pressure Variation Low
• P03D0GenericCylinder 6 Combustion Performance