P03A4

What it means

P03A4 means the engine control unit has judged that the pressure in cylinder 2 is too low. The code is defined generically, but how the pressure is measured or inferred depends on the engine. Some engines use a cylinder pressure sensor, while others estimate it from crankshaft speed variation or similar strategies. The control unit saw cylinder 2 pressure fall below the expected range for the operating conditions.

Symptoms

• Engine misfire or rough running, especially at idle
• Loss of power or sluggish acceleration
• Malfunction indicator lamp on, possibly flashing under misfire
• Hard starting or longer cranking
• Increased fuel consumption or rough, uneven exhaust note
• Possible additional misfire codes for cylinder 2

Possible causes

• Mechanical loss of compression in cylinder 2 (worn or burnt valve, valve seat, piston rings or bore wear)likely
• Leaking cylinder head gasket affecting cylinder 2possible
• Valve timing fault or valve clearance/valve actuation problem on cylinder 2possible
• Faulty cylinder pressure sensor, or damaged wiring or connector to it, where fittedpossible
• Combustion fault on cylinder 2 such as a failing injector, ignition component or fuelling problem giving low measured pressurepossible
• Crankshaft position sensor or reluctor signal fault causing a false low reading on engines that infer pressurerare
• Broken piston, damaged piston ring land or other internal engine damagerare

How to diagnose

1. Read all stored and pending codes and freeze frame data, noting engine load, speed and temperature when the fault set, and check for related misfire codes.
2. Check whether the vehicle uses a cylinder pressure sensor or an inferred method, using the manufacturer's information for that model and engine.
3. Inspect the wiring and connectors to the cylinder 2 sensor (if fitted), the crankshaft sensor and the injector and ignition components for damage, corrosion or looseness.
4. View live data for misfire counts and cylinder balance, and compare cylinder 2 with the others.
5. Swap ignition components or check injector operation on cylinder 2 to rule out a combustion fault before condemning the engine mechanically.
6. Perform a compression test on all cylinders and compare cylinder 2 with the rest and with the manufacturer's specification.
7. If compression is low, carry out a cylinder leakage test to locate the leak (valves, rings or head gasket) and check for coolant or oil contamination.
8. Check valve timing and valve clearances where applicable to the engine.

How to fix

• Repair or replace the faulty valve, valve seat, piston rings or other worn internal engine components identified by testing.
• Replace a leaking cylinder head gasket and check the head and block for flatness and damage.
• Correct valve timing or valve clearance faults and replace worn timing or valve train components.
• Repair damaged wiring or connectors, or replace a faulty cylinder pressure sensor, then confirm the readings are plausible.
• Replace faulty injectors or ignition parts on cylinder 2 if they are the cause of the low pressure reading.

Can I keep driving?

Nearby codes

• P03A3GenericCylinder 2 Pressure Sensor Circuit Intermittent/Erratic
• P03A5GenericCylinder 2 Pressure Too High