P03A5
Cylinder 2 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
- A5
- FaultThe specific fault in that area
What it means
P03A5 is the generic code for Cylinder 2 Pressure Too High. The engine control unit uses a combustion or cylinder pressure signal, or a value derived from it, and saw cylinder 2 peak pressure above the expected limit for the current load and speed. This is only used on engines that measure or model cylinder pressure, so the exact method depends on the engine.
Symptoms
- Engine warning light on
- Rough running or uneven idle
- Knocking, pinking or harsh diesel-type clatter from one cylinder
- Loss of power or limp mode
- Poor fuel economy or excess smoke
- Hard starting or hesitation under load
Possible causes
- Fuel injector on cylinder 2 over-delivering, leaking or sticking openlikely
- Pre-ignition or over-advanced combustion in cylinder 2 from heavy carbon deposits, hot spots or wrong spark pluglikely
- Cylinder pressure sensor, its wiring or connector faulty, giving a false high readingpossible
- Poor quality or wrong fuel (low octane or poor cetane) causing abnormal combustionpossible
- Excess boost or fuelling from a related fault such as a boost control or fuel pressure faultpossible
- Mechanical issue changing compression in cylinder 2, such as a modified or incorrect component or heavy deposit build-uprare
- Outdated or faulty engine control calibration, where the manufacturer has identified it as a causerare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting load, speed, temperature and boost when it set. Look for related misfire, knock, injector, fuel pressure or boost codes.
- Check the fuel in the tank for age, quality and correct grade, and ask about recent refuelling or tuning changes.
- Inspect the cylinder 2 pressure sensor wiring and connector for damage, corrosion, chafing and water ingress.
- Compare live cylinder pressure or combustion data for all cylinders to see if cylinder 2 is genuinely high or just a sensor outlier.
- Check fuel trims, rail pressure and boost against specification, and check for other faults that could raise fuelling or boost.
- Carry out an injector leak-off, balance or flow test on cylinder 2 as the engine design allows.
- Inspect the spark plug or glow plug in cylinder 2 for the correct type, overheating or deposits, and look inside the cylinder with a borescope for carbon build-up or damage.
- Carry out a compression test and, if results are abnormal, a leak-down test on cylinder 2.
How to fix
- Replace or repair the cylinder 2 injector if it is leaking or over-delivering.
- Clean carbon deposits using a procedure suitable for the engine, and fit the correct specification spark plugs or glow plugs.
- Repair the wiring or connector, or replace the cylinder pressure sensor if it is proven faulty.
- Drain contaminated fuel and refill with the correct quality and grade.
- Fix the underlying boost, fuel pressure or sensor fault that is causing excess fuelling or boost.
- Repair any mechanical fault found in cylinder 2, and apply a manufacturer calibration update only if one is published for this fault.
Can I keep driving?
High severity
Avoid driving, or keep it to a short, gentle trip to a workshop, because abnormally high cylinder pressure can damage pistons, bearings and the head gasket. Stop immediately if you hear knocking or the car goes into limp mode.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.