If an engine brake continues to function in one cylinder when the brakes are off, what is most likely defective?

• A. Master switch
• B. Circuit solenoid
• C. Brake switch
• D. Accelerator switch

Answer: (B)

Engine braking in many diesel engines is controlled by individual solenoids that energize each cylinder’s brake action. When the brakes are off, those solenoids should not be energized. If the engine brake continues to function in just one cylinder while the brakes are off, the most likely issue is that the circuit solenoid for that cylinder is stuck energized or has a fault causing it to stay active. That per-cylinder solenoid fault explains why only one cylinder continues to brake. A master switch problem would affect all cylinders, and a brake switch problem would typically alter activation for the entire system, not just a single cylinder. The accelerator switch isn’t part of the engine-brake control.