P03CC
Cylinder 6 Pressure Too Low.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 3
- AreaIgnition system or misfire
- CC
- FaultThe specific fault in that area
What it means
P03CC means the engine control unit has judged that the pressure in cylinder 6 is lower than expected. Depending on the engine, this is measured by an in-cylinder pressure sensor or inferred from crankshaft speed variation during combustion. It points to a real loss of cylinder pressure, a combustion fault on that cylinder, or a fault in the pressure measurement circuit.
Symptoms
- Engine management light on
- Rough idle or a noticeable misfire
- Loss of power, especially under load
- Hesitation or uneven running on acceleration
- Increased fuel consumption or a fuel smell from the exhaust
- Hard starting or extended cranking
Possible causes
- Mechanical loss of compression in cylinder 6, such as a burnt or leaking valve, worn piston rings or cylinder wall damagelikely
- Combustion fault on cylinder 6 from a failed ignition coil, worn spark plug or faulty fuel injector causing weak or no combustionlikely
- Head gasket leak or cracked head affecting cylinder 6possible
- Faulty cylinder pressure sensor, damaged wiring or poor connector contact (only on engines fitted with one)possible
- Valve timing or camshaft phasing fault, or a valve not seating due to carbon deposits or a sticking valvepossible
- Restricted intake or exhaust flow affecting only cylinder 6, or a control unit software faultrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting engine load, speed and temperature when the code set; look for related misfire codes, especially for cylinder 6.
- Check the engine oil and coolant levels and condition, looking for fuel dilution, coolant contamination or white exhaust smoke.
- Inspect the wiring and connectors for cylinder 6 and for any cylinder pressure sensor fitted, looking for chafing, corrosion, oil ingress or loose pins.
- Review live data for misfire counters and fuel trims, and check whether the fault follows load or engine temperature.
- Inspect the cylinder 6 spark plug, then swap the coil, and the injector where practical, with another cylinder to see if the fault moves.
- Carry out a compression test on all cylinders and compare cylinder 6 against the others; follow with a leakdown test if it is low.
- Check for combustion gases in the coolant and inspect the cylinder with a borescope for valve, piston or bore damage.
- Check valve timing and camshaft correlation against the manufacturer's data for that engine, as the procedure varies by model.
How to fix
- Replace a faulty ignition coil, spark plug or fuel injector on cylinder 6 as confirmed by testing.
- Repair or replace damaged wiring, connectors or a failed cylinder pressure sensor where fitted.
- Repair or replace the head gasket and check the head for flatness and cracks if a leak is confirmed.
- Repair valves, valve seats or piston rings, or overhaul the engine, if the compression or leakdown test confirms mechanical wear.
- Correct valve timing or camshaft phasing faults, and clean carbon deposits where they stop the valves seating.
- Apply a manufacturer software update only if a known fault in the calibration is documented for that engine.
Can I keep driving?
Short, gentle driving to a workshop is usually acceptable, but avoid heavy loads and high revs. Stop driving if the engine runs very roughly, the engine management light flashes, or there is overheating or heavy smoke, as unburnt fuel can damage the catalytic converter and a mechanical fault can worsen.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.