P0278

What P0278 Means

Code P0278 indicates a contribution imbalance from cylinder 6 in the engine's overall operation. The DME (engine control unit) detects that cylinder No. 6 is producing less power than the others. This isn't a specific component failure but a general symptom that can have several causes.

The injection and ignition system runs under DME control, which monitors crankshaft rotational uniformity. When cylinder operation deviates from target values, the control unit sets the fault code. The most likely causes are a faulty fuel injector, low compression in the cylinder, or other issues affecting air-fuel mixture filling and combustion.

Symptoms

• Misfires, especially noticeable at idle and under load.
• Uneven idle (single-cylinder misfire feel, vibration).
• Power loss during acceleration and under load.
• Check Engine light on the instrument cluster.

Diagnosis and Repair

1. Read fault codes with diagnostic equipment (ISTA, INPA) and check for related misfire codes.
2. Check the cylinder 6 fuel injector: measure winding resistance, check the control signal from the DME, and run an injector performance test if possible.
3. Perform a compression test on cylinder No. 6. Low compression points to mechanical problems (worn piston rings, valves, a burned piston, and so on).
4. If the injector is confirmed faulty, replace the injector.
5. After repair, clear the codes and take a test drive to confirm the fault doesn't return.

Long-Term Damage and Consequences

Prolonged operation with code P0278 and related misfires can lead to the following:

• Increased catalytic converter wear from unburned fuel entering the exhaust system.
• Spark plug and ignition coil damage in the affected cylinder.
• Worse fuel economy and higher exhaust emissions.
• With low compression, further progression of the mechanical fault (bore scoring, burned valves). Left alone, that means an engine-out repair bill.

Don't put off diagnosing and fixing the cause of the cylinder imbalance.