Worn, fouled or incorrectly gapped spark plug on cylinder 6 (petrol engines); Faulty ignition coil or coil connector on cylinder 6; Faulty, blocked or leaking fuel injector on cylinder 6; Low compression in cylinder 6 from valve, piston ring or head gasket wear or damage; Vacuum or intake leak affecting cylinder 6, or carbon build-up on intake valves; Wiring or connector fault in the injector or ignition circuit for cylinder 6; Glow plug, injector or EGR-related issue on cylinder 6 (diesel engines, depending on model).

P03D0

Cylinder 6 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
D0: FaultThe specific fault in that area

What it means

P03D0 is a generic code meaning the engine control unit has detected that combustion in cylinder 6 is not performing as expected. It is typically set when crankshaft speed analysis or other monitoring shows that cylinder 6 is contributing less (or more erratically) than the other cylinders, without necessarily being a full misfire. The exact detection method and thresholds vary by manufacturer and engine.

Symptoms

Rough or uneven idle
Hesitation or reduced power under load
Engine management light on, possibly flashing if misfire develops
Increased fuel consumption
Vibration or shake at certain engine speeds
Smell of unburnt fuel from the exhaust

Possible causes

Worn, fouled or incorrectly gapped spark plug on cylinder 6 (petrol engines)likely
Faulty ignition coil or coil connector on cylinder 6likely
Faulty, blocked or leaking fuel injector on cylinder 6likely
Low compression in cylinder 6 from valve, piston ring or head gasket wear or damagepossible
Vacuum or intake leak affecting cylinder 6, or carbon build-up on intake valvespossible
Wiring or connector fault in the injector or ignition circuit for cylinder 6possible
Glow plug, injector or EGR-related issue on cylinder 6 (diesel engines, depending on model)rare

How to diagnose

Read all stored and pending codes and freeze frame data, noting engine load, speed and temperature when the fault set
Check for related misfire codes (P0306 or others) and any fuel trim or injector circuit codes
Inspect the wiring and connectors at the cylinder 6 coil and injector for damage, corrosion or looseness
Remove and inspect the cylinder 6 spark plug (petrol), comparing its condition with the other cylinders
Swap the cylinder 6 coil with another cylinder and see whether the fault follows it
Check live data for misfire counters and injector balance or correction values, if the vehicle supports them
Test for intake or vacuum leaks, for example with a smoke test
Carry out a compression or cylinder leak-down test on cylinder 6 if the cheaper checks do not find the cause

How to fix

Replace the spark plugs in the set to the correct specification and gap
Replace the faulty ignition coil on cylinder 6
Clean or replace the faulty fuel injector on cylinder 6
Repair or replace damaged wiring or connectors in the affected circuit
Repair intake leaks and clean carbon deposits where confirmed as the cause
Carry out the necessary engine repair if compression testing shows mechanical wear or damage

Can I keep driving?

Medium severity

Short, gentle journeys are usually possible, but get it checked soon as continued poor combustion can overheat and damage the catalytic converter. If the warning light flashes or the engine runs very roughly, stop driving and have the car recovered.

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