P03A6

What it means

P03A6 means the engine control unit has detected that the combustion pressure variation on cylinder 2 is lower than expected. It is set by comparing the cylinder's measured or calculated pressure against the expected value or the other cylinders. This only applies to engines that monitor cylinder pressure, so how it is measured depends on the model and engine.

Symptoms

• Rough idle or uneven running
• Misfire or hesitation under load
• Reduced power or poor throttle response
• Engine management light on
• Increased fuel consumption or poor economy
• Harder starting in some cases

Possible causes

• Weak combustion in cylinder 2 from an ignition fault (worn spark plug, faulty coil) on petrol engineslikely
• Faulty or leaking fuel injector on cylinder 2, or poor fuel delivery to that cylinderlikely
• Faulty cylinder pressure sensor, or damaged wiring or connector to it, where fittedpossible
• Low compression in cylinder 2 (worn rings, burnt or leaking valve, head gasket leak)possible
• Intake air leak or carbon build-up affecting cylinder 2 airflowpossible
• Valve timing or valve train fault, such as worn cam lobe or sticking valverare
• Outdated or faulty engine control unit calibration where the manufacturer has issued a known updaterare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting load, engine speed and temperature when the code set.
2. Check for related misfire, fuel trim, injector or cylinder pressure sensor codes, as these point to the root cause.
3. Inspect the wiring and connectors for cylinder 2, including the sensor, injector and coil, for damage, corrosion or water ingress.
4. Check live misfire counters and cylinder balance data to confirm whether cylinder 2 is the weak cylinder.
5. Inspect the spark plug and coil on cylinder 2 (petrol), or test the injector operation and balance, following the manufacturer's procedure.
6. Check for intake air leaks and inspect the intake for carbon build-up or restriction.
7. Carry out a compression or cylinder leak-down test on cylinder 2 to rule out mechanical wear or sealing faults.
8. Check for any manufacturer service bulletins or calibration updates for your model and engine.

How to fix

• Replace worn spark plugs or a faulty ignition coil on cylinder 2.
• Repair or replace a faulty injector, or correct the fuel delivery problem.
• Repair damaged wiring or connectors, or replace a faulty cylinder pressure sensor where fitted.
• Repair the engine mechanical fault found, such as valve, piston ring or head gasket work.
• Fix intake leaks and clean or clear carbon build-up as the model's procedure allows.
• Apply an official control unit calibration update only if one is known to address this fault.

Can I keep driving?

Nearby codes

• P03A5GenericCylinder 2 Pressure Too High
• P03A7GenericCylinder 2 Pressure Variation High