Engine

P03CF — Cylinder 6 Pressure Variation Too High

Severity: medium Drive with care, to a shop

What P03CF means

The engine control module monitors how evenly each cylinder fires, for example through crankshaft speed changes. With P03CF it found that cylinder 6 shows more pressure variation than allowed. This usually points to unstable combustion or a misfire caused by weak spark, poor fuel delivery, or lost compression.

Symptoms

  • Check engine light on or flashing
  • Rough running or misfire
  • Poor acceleration and low power
  • Worse fuel economy
  • Shaking at idle

Possible causes

  1. Worn spark plug or failing ignition coil on cylinder 6
  2. Faulty or clogged fuel injector on cylinder 6
  3. Low fuel pressure
  4. Compression loss in cylinder 6: valves, rings, or head gasket
  5. Damaged wiring or connector at the coil or injector
  6. Vacuum leak near cylinder 6

How to diagnose

  1. Scan all codes and freeze frame data, and look for misfire codes such as P0306
  2. Inspect the cylinder 6 spark plug and coil for wear, gap, and damage
  3. Swap the coil with another cylinder and see if the fault follows
  4. Check coil and injector connectors and wiring for power and ground
  5. Test the injector's resistance and operation
  6. Measure fuel pressure
  7. Inspect the intake for vacuum leaks
  8. Run a compression or cylinder leakdown test

Common fixes

  • Replace the spark plug and/or ignition coil for cylinder 6
  • Clean or replace the injector, or fix the fuel pressure problem
  • Repair the wiring or connector
  • Do engine mechanical repair: valves, piston rings, or head gasket

Questions and answers

What does P03CF mean?

The ECM detected too much pressure variation in cylinder 6. It is most often tied to a misfire from the spark plug, coil, injector, or poor compression.

Can I drive with P03CF?

Only briefly and gently, to reach a repair shop. Misfires can damage the catalytic converter, and if the check engine light flashes you should stop driving.

Where should I start diagnosing P03CF?

Start with the cylinder 6 spark plug and coil. Swap the coil with a neighboring cylinder and see if the code follows; if not, check the injector and 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.