What it means
Cylinder 5 measured peak combustion pressure is below the calibrated minimum — typically low compression, weak injection, or stuck-open exhaust valve.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The cylinder 5 pressure sensor measures the pressure produced during combustion, allowing the controller to compare that cylinder's firing with its expected performance. P03C2 sets when cylinder 5's measured peak pressure falls below the calibrated minimum, which can result from poor sealing or insufficient fuel delivery.
Common causes
Most likely first.
- Low compression in cylinder 5
- Fuel injector delivering too little fuel
- Leaking or stuck-open valve
- Worn or damaged piston rings
Symptoms
- Check-engine light
- Rough running or misfire
- Reduced engine power
- Increased fuel consumption
How to diagnose it
- Confirm P03C2 and record freeze-frame data, then check for related misfire, injector, or pressure-sensor codes.
- Review live cylinder pressure and misfire data to see whether cylinder 5 stays low under the conditions captured in the freeze frame.
- Inspect the cylinder 5 sensor connector and harness to rule out a signal problem that could imitate low combustion pressure.
- Check cylinder 5 injector operation and delivery using the vehicle's specified diagnostic procedure.
- If the signal and fuel delivery are sound, perform a compression or leak-down assessment on cylinder 5 and compare results with the manufacturer's specification.
Common fixes
- Repair a loose or damaged cylinder 5 pressure-sensor connection if its signal is unreliable.
- Restore proper fuel delivery by repairing or replacing a confirmed faulty cylinder 5 injector.
- Repair a leaking valve or other cylinder 5 sealing fault identified by testing.
- Repair worn or damaged cylinder 5 piston rings if compression testing confirms leakage past the rings.
Can I keep driving?
A brief, gentle trip may be possible, but avoid hard acceleration, towing, and extended driving if the engine is rough or down on power. Continued low combustion pressure can worsen misfiring, fuel use, and emissions, and may lead to further engine or exhaust damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.