P0278 indicates that the engine control module has detected an imbalance in the contribution of cylinder 6 to overall engine output, usually due to a fuel delivery or combustion issue in that cylinder. The PCM monitors each cylinder's power contribution via crankshaft speed variations and sets the code when cylinder 6 consistently underperforms.
The injector may be clogged, stuck open/closed, or have an internal electrical fault, causing insufficient or excessive fuel delivery.
Corrosion, broken wires, or loose pins in the injector harness can interrupt the signal or power to the injector.
A weak spark can reduce combustion efficiency, making the cylinder appear to contribute less power.
Worn piston rings, leaking valves, or a head gasket leak can lower cylinder pressure and power output.
An exhaust leak can cause false lean/rich signals that the PCM interprets as a contribution imbalance.
Although technically possible, a faulty PCM is a rare cause of P0278 and should be considered only after all other components are verified.
No. PCM failure is uncommon for this code; the majority of cases are due to a faulty injector, wiring issue, or ignition/compression problem in cylinder 6.
Driving may cause rough running, reduced power, and potential catalyst damage from unburned fuel; it is advisable to diagnose and repair the issue promptly.
Typically only the injector that is faulty for cylinder 6 needs replacement; other injectors should be inspected but not replaced unless they also show faults.
Clearing the code only turns off the check‑engine light; the underlying fault will remain and the code will likely return.