Weak or faulty combustion in cylinder 3 from a worn spark plug, faulty ignition coil or failing injector; Low mechanical compression on cylinder 3, such as a burnt or leaking valve, worn piston rings or a head gasket leak; Wiring or connector fault, or a faulty cylinder pressure sensor or its circuit, on engines fitted with one; Injector fault on cylinder 3 causing a lean, rich or poorly atomised fuel delivery; Intake air leak or carbon build-up affecting cylinder 3 airflow, particularly on direct injection engines; Valve timing fault or a problem with the valve train on cylinder 3, such as a worn cam lobe or a collapsed lifter; Outdated or faulty engine control unit calibration where the manufacturer has issued a known fix.

P03B0

Cylinder 3 Pressure Variation Low.

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
B0: FaultThe specific fault in that area

What it means

P03B0 is the generic SAE J2012 code for Cylinder 3 Pressure Variation Low. The engine control unit has judged that the combustion or cylinder pressure on cylinder 3 is lower than expected, or varies less than the other cylinders or the expected value. How it measures this depends on the engine. Some use an in-cylinder pressure sensor, while others infer it from crankshaft speed or other signals. The exact detection method and thresholds vary by model and engine.

Symptoms

Engine management light on
Rough idle or a noticeable misfire-like shake
Loss of power or flat acceleration
Poor fuel economy
Hesitation or uneven running under load
Possible additional misfire codes for cylinder 3

Possible causes

Weak or faulty combustion in cylinder 3 from a worn spark plug, faulty ignition coil or failing injectorlikely
Low mechanical compression on cylinder 3, such as a burnt or leaking valve, worn piston rings or a head gasket leakpossible
Wiring or connector fault, or a faulty cylinder pressure sensor or its circuit, on engines fitted with onepossible
Injector fault on cylinder 3 causing a lean, rich or poorly atomised fuel deliverypossible
Intake air leak or carbon build-up affecting cylinder 3 airflow, particularly on direct injection enginespossible
Valve timing fault or a problem with the valve train on cylinder 3, such as a worn cam lobe or a collapsed lifterrare
Outdated or faulty engine control unit calibration where the manufacturer has issued a known fixrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including engine load, speed and temperature when the fault set.
Check for related codes such as misfire on cylinder 3, injector, ignition or cylinder pressure sensor faults, and deal with those first.
Visually inspect the wiring and connectors for cylinder 3 (coil, injector and pressure sensor if fitted) for damage, corrosion, chafing or heat damage.
Remove and inspect the cylinder 3 spark plug and compare it with the others, and swap the coil with another cylinder to see if the fault follows.
Check live data for misfire counters and fuel trims, and look for an air leak near cylinder 3 with a visual check and a smoke test.
Test the injector on cylinder 3 for resistance and operation as per the manufacturer's data for your engine.
Carry out a compression test or cylinder leak-down test on cylinder 3 and compare it with the other cylinders.
Check for a manufacturer service bulletin or calibration update relevant to this engine and code.

How to fix

Replace the worn spark plug or faulty ignition coil on cylinder 3.
Repair or replace the faulty injector, or clean it if the manufacturer's procedure allows.
Repair damaged wiring or connectors, or replace the cylinder pressure sensor if testing proves it faulty.
Fix any intake air leak and clean carbon build-up using the manufacturer's recommended method.
Repair the engine mechanically if compression or leak-down tests show a fault, such as valve, ring, head gasket or valve train work.
Apply a manufacturer calibration update only if a known issue is confirmed for your engine.

Can I keep driving?

Medium severity

Short, gentle driving is usually possible, but get it checked soon. If the engine is misfiring badly, the warning light flashes or power is greatly reduced, stop driving, as unburnt fuel can damage the catalytic converter and low compression may indicate engine damage.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.