How are ERG valves controlled?

ERG valves, or Exhaust Gas Recycling valves, are primarily controlled by either vacuum pressure or electrical signals. This method of operation allows for precise regulation of exhaust gases that are redirected back into the engine's intake.

When the engine is running and the conditions are appropriate, a vacuum is created that opens the valve to allow a certain amount of exhaust gas to re-enter the intake system. This helps to reduce nitrogen oxide emissions and improve engine efficiency. In modern systems, electronic control units (ECUs) also manage ERG valve operation by sending electrical signals to actuate the valve, providing more responsive and precise control based on real-time engine conditions.

Manual adjustments or control solely by fluid pressure do not provide the necessary responsiveness and precision required for optimal engine operation and emissions control. Therefore, the combination of vacuum and electrical methods represents the most effective and commonly used approach for controlling ERG valves, making that the correct answer.