P03B2

What it means

P03B2 is a generic code meaning the engine control unit has judged that combustion in cylinder 3 is not performing as expected. It usually comes from crankshaft speed analysis or other combustion-quality monitoring, which shows that cylinder contributing less (or inconsistently) compared with the others. The exact detection method and thresholds vary by manufacturer and engine.

Symptoms

• Rough idle or a noticeable engine shake
• Hesitation or reduced power under load
• Malfunction indicator lamp on, possibly flashing if misfire is severe
• Hard starting or uneven running when cold
• Raised fuel consumption
• Smell of unburnt fuel from the exhaust

Possible causes

• Worn or faulty spark plug or ignition coil on cylinder 3 (petrol engines)likely
• Faulty or leaking fuel injector on cylinder 3, or a glow plug/injector fault on dieselslikely
• Vacuum or intake air leak affecting cylinder 3, such as a damaged intake manifold gasket or cracked hosepossible
• Poor compression in cylinder 3 from a burnt valve, worn piston rings or damaged head gasketpossible
• Wiring or connector fault in the ignition or injector circuit for cylinder 3possible
• Carbon build-up on intake valves or a sticking valve or injector affecting cylinder 3possible
• Crankshaft position sensor or reluctor wheel fault causing false combustion readingsrare

How to diagnose

1. Read all stored codes and freeze frame data, noting engine load, temperature and speed when the fault set, and check for other misfire or fuel trim codes
2. Check for any manufacturer service bulletins or known issues for the specific engine
3. Inspect the wiring and connectors to the cylinder 3 coil and injector for damage, corrosion or water ingress
4. Remove and inspect the cylinder 3 spark plug (petrol) and compare it with the other cylinders
5. Swap the cylinder 3 coil with another cylinder and see whether the fault follows it
6. Check injector operation and balance on cylinder 3, for example by resistance test, waveform or flow check
7. Smoke test the intake for leaks and inspect hoses and gaskets near cylinder 3
8. Carry out a compression or leak-down test on cylinder 3 if the ignition and fuel side check out

How to fix

• Replace the worn spark plugs and/or the faulty ignition coil, as a set where appropriate
• Replace or professionally clean and test the faulty injector on cylinder 3
• Repair the damaged wiring or connector, or seal the intake leak
• Clean carbon deposits from the intake tract or valves if confirmed as the cause
• Repair the mechanical fault, such as valve, piston ring or head gasket work, if compression is low
• Replace a faulty crankshaft sensor only if testing confirms it is at fault

Can I keep driving?

Nearby codes

• P03B1GenericCylinder 3 Pressure Variation High
• P03B3GenericCylinder 4 Pressure Sensor Circuit