How are engine brakes controlled?

Typically, under good road conditions, the driver enables the retarder and selects a level of retarding with selector switches on the dash. To activate the brake, two more conditions must be met: clutch is engaged (or automatic transmission is in lock-up), and no fuel to the engine (foot off the pedal). Under these conditions, voltage is applied to the engine brake solenoids, and the brake is activated. On older engines with mechanical fuel control, the Jacobs Engine Brake control system includes fuel pump and clutch switches in addition to the dash switches to detect when the required conditions were met. Today's electronic engines have an engine control module (ECM) which knows when there is a no fuel condition, and many have inputs to tell them if the clutch is engaged. For electronic engines the engine brake is powered directly by the engine control module. All engine brake control systems can be configured to work with a vehicle's ABS brake system, and most can be configured to wo ... more