Abnormal combustion in cylinder 5 such as pre-ignition or knock, caused by hot carbon deposits, wrong fuel or a worn spark plug; Faulty or contaminated cylinder 5 pressure sensor, or its signal being out of range; Wiring or connector fault on the cylinder 5 pressure sensor circuit (chafing, corrosion, poor pin contact); Cylinder 5 injector fault delivering too much fuel or leaking, giving an over-rich or abnormal burn; Excess boost pressure or over-advanced ignition or injection timing from a boost control or timing fault; Heavy carbon build-up in cylinder 5 raising compression ratio, or a mechanical fault such as head gasket or piston damage; Outdated or faulty engine control unit calibration, where the manufacturer has identified this as a known cause for the engine.

P03C3

Cylinder 5 Pressure Too High.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
C3: FaultThe specific fault in that area

What it means

P03C3 is a generic code meaning the engine control unit has judged the pressure in cylinder 5 to be higher than expected. It is set from a cylinder pressure signal, or from a calculated value based on it, that exceeded the permitted limit for the current load and speed. Only some engines have in-cylinder pressure monitoring, so exactly how the pressure is measured and what limit applies depends on the model and engine.

Symptoms

Engine warning light on, possibly flashing or with a reduced power message
Pinking, knocking or rattling noises under load
Rough running or misfire on cylinder 5
Reduced power or limp mode
Rough or unstable idle
Higher fuel consumption or hesitation

Possible causes

Abnormal combustion in cylinder 5 such as pre-ignition or knock, caused by hot carbon deposits, wrong fuel or a worn spark pluglikely
Faulty or contaminated cylinder 5 pressure sensor, or its signal being out of rangelikely
Wiring or connector fault on the cylinder 5 pressure sensor circuit (chafing, corrosion, poor pin contact)possible
Cylinder 5 injector fault delivering too much fuel or leaking, giving an over-rich or abnormal burnpossible
Excess boost pressure or over-advanced ignition or injection timing from a boost control or timing faultpossible
Heavy carbon build-up in cylinder 5 raising compression ratio, or a mechanical fault such as head gasket or piston damagerare
Outdated or faulty engine control unit calibration, where the manufacturer has identified this as a known cause for the enginerare

How to diagnose

Read all stored and pending codes and the freeze frame data; note load, rpm, boost and temperature when the code set, and look for related misfire, knock, boost or injector codes
Check the fuel level and quality, and ask when it was last refuelled and whether the wrong fuel could have been used
Inspect the cylinder 5 pressure sensor wiring and connector for damage, corrosion, moisture and poor pin tension
Check live data for cylinder 5 pressure against the other cylinders at idle and under load, and watch for knock activity or misfire counters on cylinder 5
Check spark plug condition and heat range on cylinder 5 (petrol), or the injector balance and correction values (diesel)
Compare actual and requested boost, and check ignition or injection timing values for anything abnormal
Check for relevant manufacturer service bulletins or calibration updates for the engine in question
If the cause is still unclear, carry out a compression test and a borescope inspection of cylinder 5 for deposits or damage

How to fix

Repair or replace damaged wiring or connectors on the cylinder 5 pressure sensor circuit
Replace the cylinder 5 pressure sensor if its signal is confirmed faulty or implausible
Replace worn or incorrect spark plugs, or a faulty or leaking injector on cylinder 5
Correct the boost control or timing fault found, such as a sticking wastegate or faulty sensor
Remove carbon deposits using the manufacturer's approved procedure, and repair any mechanical damage found
Apply a calibration update only if the manufacturer lists it as the fix for this fault on your engine

Can I keep driving?

High severity

Limit driving as far as possible, because excessive cylinder pressure can damage pistons, bearings and the head gasket. If the engine is knocking, running roughly or in limp mode, stop and have the car recovered rather than driving it.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.