P03A8
Cylinder 2 Combustion Performance.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 3
- AreaIgnition system or misfire
- A8
- FaultThe specific fault in that area
What it means
P03A8 means the engine control unit has judged that combustion in cylinder 2 is not performing as expected. Depending on the engine, it detects this through crankshaft speed variation, in-cylinder pressure or ion current monitoring, or other combustion quality measures. Cylinder 2 is producing less (or inconsistent) output than the other cylinders. The exact monitoring method and thresholds depend on the vehicle and engine.
Symptoms
- Rough idle or noticeable engine shake
- Misfire feel, hesitation or jerking under load
- Engine management light on, possibly flashing under heavy load
- Loss of power and poor fuel economy
- Hard starting or uneven running when cold
- Smell of unburnt fuel from the exhaust
Possible causes
- Worn, fouled or incorrectly gapped spark plug on cylinder 2 (petrol engines)likely
- Faulty ignition coil or coil wiring/connector on cylinder 2likely
- Faulty, leaking or blocked fuel injector on cylinder 2likely
- Vacuum or intake leak near cylinder 2, such as a cracked manifold seal or hosepossible
- Low or uneven compression in cylinder 2 (worn rings, burnt valve, head gasket leak)possible
- Wiring or connector fault in the injector or ignition circuit, or a faulty in-cylinder sensor where fittedpossible
- Valve train problem such as a worn cam lobe, sticking valve or incorrect valve timingrare
How to diagnose
- Read all stored and pending codes and the freeze frame data (engine speed, load, temperature) to see when the fault occurs, and check for other misfire or fuel trim codes.
- Check live data for cylinder 2 misfire counts or combustion quality values and compare them with the other cylinders.
- Inspect the cylinder 2 coil, plug lead (where fitted), injector connector and wiring for damage, corrosion, oil or heat damage.
- Remove and inspect the cylinder 2 spark plug for wear, deposits, oil, fuel or damage, and check the gap against the manufacturer's specification.
- Swap the cylinder 2 coil with another cylinder and see whether the fault follows the coil; do the same test with the injector if the engine layout allows.
- Check for intake leaks around the manifold and hoses, and look at fuel trims for signs of a lean condition.
- Test fuel pressure and injector operation or balance, following the procedure for that engine.
- Carry out a compression or leak-down test on cylinder 2 if the ignition and fuel checks do not find the fault.
How to fix
- Replace the cylinder 2 spark plug (usually best done as a full set) with the correct specification.
- Replace the faulty ignition coil on cylinder 2 and repair any damaged coil wiring or connector.
- Clean or replace the cylinder 2 injector, or repair its wiring or connector, as testing shows.
- Repair intake leaks by replacing the faulty gasket, seal or hose.
- Carry out the mechanical repair indicated by compression or leak-down results, such as valve, piston ring or head gasket work.
- Repair or replace the cylinder 2 combustion sensor or its wiring on engines that use one, and clear the code only after the repair is confirmed.
Can I keep driving?
Short, gentle journeys to a workshop are usually acceptable, but avoid heavy loads and high revs. If the warning light flashes or the engine runs very roughly, stop driving, as unburnt fuel can damage the catalytic converter.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.