Engine

P03CC — Cylinder 6 Pressure Too Low

Severity: medium Drive with care, to a shop

What P03CC means

The engine control module found that cylinder 6 pressure is lower than expected. It reads this from an in-cylinder pressure sensor if the engine has one, or infers it from crankshaft speed variations. Low pressure points to weak combustion or a cylinder that is not sealing well.

Symptoms

  • Check engine light on
  • Rough idle
  • Hesitation or loss of power
  • Higher fuel consumption
  • Engine vibration or misfires

Possible causes

  1. Worn spark plug or failing ignition coil on cylinder 6
  2. Clogged or faulty fuel injector on cylinder 6
  3. Low mechanical compression: worn rings, burned or leaking valve, head gasket damage
  4. Vacuum leak or intake air imbalance near cylinder 6
  5. Faulty cylinder pressure sensor or its wiring, if equipped

How to diagnose

  1. Scan for all codes and freeze frame data, and look for misfire codes such as P0306
  2. Inspect the cylinder 6 spark plug and coil; swap the coil with a neighbor to see if the fault follows
  3. Test the cylinder 6 injector: resistance, operating sound, and flow balance
  4. Check the intake for vacuum leaks and review fuel trim values
  5. If fitted, check the cylinder pressure sensor connector, wiring, and supply voltage
  6. Run a compression test or a cylinder leak-down test
  7. If a head gasket is suspected, check the coolant for combustion gases and the plug for oil or coolant

Common fixes

  • Replace the spark plug or ignition coil on cylinder 6
  • Clean or replace the cylinder 6 injector
  • Repair vacuum leaks and replace damaged hoses or gaskets
  • Repair the wiring or replace the cylinder pressure sensor
  • Do engine mechanical repair (rings, valves, head gasket) if compression is low

Questions and answers

What does P03CC mean?

The ECM sees lower than expected pressure in cylinder 6. It is most often caused by ignition or fuel delivery problems, and less often by engine mechanical wear.

Can I drive with P03CC?

Only for a short distance under light load to reach a shop. If the check engine light is flashing, stop driving to avoid damaging the catalytic converter.

Where should I start diagnosing P03CC?

Start with the cylinder 6 spark plug and coil, then check the injector. If both are fine, test the cylinder compression.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.