Faulty injector or fuelling fault on cylinder 3 (over-fuelling, leaking or sticking injector, or incorrect injection timing); Abnormal combustion on cylinder 3, such as pre-ignition or knock from carbon deposits, hot spots, wrong spark plug heat range or poor fuel quality; Faulty cylinder 3 pressure sensor or its wiring, connector or reference supply giving a false high reading; Ignition timing or boost pressure control fault raising peak cylinder pressure (for example, overboost or a faulty actuator); Excessive compression from heavy carbon build-up in the combustion chamber or an incorrect cylinder head gasket thickness after previous work; Outdated or faulty control unit software or calibration, where a manufacturer bulletin lists it as a cause.

P03AF

Cylinder 3 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
AF: FaultThe specific fault in that area

What it means

P03AF means the engine control unit has judged that the pressure in cylinder 3 is higher than expected. Only engines fitted with in-cylinder pressure monitoring (a pressure sensor or a calculated pressure value) can set it, and how it is measured depends on the model and engine. Either the combustion pressure reading exceeded its limit, or the signal is implausible compared with other cylinders and the expected value for the load.

Symptoms

Engine warning light on, possibly with the engine in reduced power mode
Rough running, knocking, pinking or harsh combustion noise from the engine
Hesitation or uneven power under load
Misfire codes or knock-related codes stored alongside it
Poor fuel economy or hard starting

Possible causes

Faulty injector or fuelling fault on cylinder 3 (over-fuelling, leaking or sticking injector, or incorrect injection timing)likely
Abnormal combustion on cylinder 3, such as pre-ignition or knock from carbon deposits, hot spots, wrong spark plug heat range or poor fuel qualitylikely
Faulty cylinder 3 pressure sensor or its wiring, connector or reference supply giving a false high readingpossible
Ignition timing or boost pressure control fault raising peak cylinder pressure (for example, overboost or a faulty actuator)possible
Excessive compression from heavy carbon build-up in the combustion chamber or an incorrect cylinder head gasket thickness after previous workpossible
Outdated or faulty control unit software or calibration, where a manufacturer bulletin lists it as a causerare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting load, engine speed and temperature when the fault was set
Check for other related codes (misfire, knock, injector, boost, pressure sensor circuit) and look up any manufacturer bulletins for the model and engine
Inspect the cylinder 3 sensor, injector and ignition component wiring and connectors for damage, corrosion, chafing or oil contamination
Check the fuel used and the service history, looking for poor quality fuel, wrong spark plugs or recent engine work
Compare live data for cylinder 3 with the other cylinders at idle and under load, including pressure values, misfire counters, injector corrections and timing
Check boost pressure and ignition timing control against specification for signs of overboost or over-advance
Swap or test the cylinder 3 injector and ignition component against another cylinder to see whether the fault follows it
Carry out a compression test and a borescope inspection of cylinder 3 for carbon build-up, hot spots or piston and valve damage

How to fix

Repair or replace a faulty cylinder 3 injector, or correct the fuelling fault, following the manufacturer's procedure
Replace the cylinder 3 pressure sensor or repair its wiring and connectors if the signal is shown to be false
Clean or remove carbon deposits using an approved procedure, and fit the correct spark plugs or fuel if these were at fault
Repair the boost control or ignition timing fault that is raising peak cylinder pressure
Repair any mechanical fault found in cylinder 3, such as damaged piston or head gasket issues
Update the control unit software only where the manufacturer lists an outdated calibration as the cause

Can I keep driving?

High severity

Limit driving and avoid heavy load until it has been diagnosed, because excessive cylinder pressure can damage pistons, bearings and the head gasket. If the engine knocks or runs roughly, stop driving and have it recovered.

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