Faulty or worn spark plug or ignition coil on cylinder 6 (petrol engines); Faulty, blocked or leaking fuel injector on cylinder 6; Wiring or connector fault in the injector or coil circuit for cylinder 6, such as chafing, corrosion or a loose pin; Vacuum or intake air leak affecting cylinder 6, such as a split intake hose or leaking manifold gasket; Low compression on cylinder 6 from a valve, piston ring or head gasket problem; Poor fuel quality or low fuel pressure causing weak combustion; Fault in the engine control unit driver for the cylinder 6 output.

P0278

Cylinder 6 Contribution/Balance.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
78: FaultThe specific fault in that area

What it means

P0278 means the engine control unit has found that cylinder 6 is contributing less power than the other cylinders during the cylinder balance (contribution) monitoring. It usually sets from crankshaft speed variation that points to weak combustion or a misfire on that cylinder, or from a fault in the circuit controlling it. The exact way the test is run and the fault is judged varies by engine and manufacturer.

Symptoms

Rough running or a noticeable shake at idle
Loss of power and hesitation under acceleration
Engine management light on, possibly flashing under load
Increased fuel consumption
Difficult starting or uneven idle when cold
Misfire codes for cylinder 6 stored alongside it

Possible causes

Faulty or worn spark plug or ignition coil on cylinder 6 (petrol engines)likely
Faulty, blocked or leaking fuel injector on cylinder 6likely
Wiring or connector fault in the injector or coil circuit for cylinder 6, such as chafing, corrosion or a loose pinpossible
Vacuum or intake air leak affecting cylinder 6, such as a split intake hose or leaking manifold gasketpossible
Low compression on cylinder 6 from a valve, piston ring or head gasket problempossible
Poor fuel quality or low fuel pressure causing weak combustionrare
Fault in the engine control unit driver for the cylinder 6 outputrare

How to diagnose

Read all stored and pending codes and review the freeze frame data for engine speed, load and temperature when the fault set
Check for related misfire codes and fuel trim data to see whether the fault points to a lean, rich or ignition problem
Visually inspect the wiring, connectors and earth points for the cylinder 6 coil and injector, and check the intake for splits or leaks
Remove and inspect the cylinder 6 spark plug (petrol engines) for wear, fouling or damage
Swap the coil with another cylinder and see if the fault follows it, then repeat with the injector where the engine allows
Test the injector resistance and operation and the control signal at the connector against the manufacturer's specification
Check fuel pressure and look for intake leaks using a smoke test
Carry out a compression or leak-down test on cylinder 6 if the electrical and fuel checks are good

How to fix

Replace the worn spark plugs or the faulty ignition coil on cylinder 6
Clean or replace the faulty fuel injector on cylinder 6
Repair damaged wiring or connectors in the cylinder 6 circuit
Replace split hoses or leaking manifold gaskets to cure the air leak
Repair the engine mechanical fault found by compression testing, such as valves, rings or head gasket
Correct any fuel pressure or fuel quality problem found

Can I keep driving?

Medium severity

The car can usually be driven gently for a short time to get it checked, but have it looked at soon. If the warning light flashes or the engine runs very roughly, stop driving, as unburnt fuel can overheat and damage the catalytic converter.

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