What will cause an engine braking system to operate only in the first and third stages?

The engine braking system is designed to engage at specific stages to help slow down the vehicle without relying solely on the traditional braking system. If the system only operates in the first and third stages, it suggests that there is an issue with the activation mechanism or control that governs the stages of engine braking.

A faulty dash switch can disrupt the signals sent to the engine braking system, which is generally activated by the driver's input through the dashboard controls. If this switch is malfunctioning, it may not properly initiate the second stage of braking, which would mean that the system only engages during the first and third stages as designed.

The other components mentioned, such as the brake switch, clutch switch, and throttle switch, play different roles in vehicle operation. The brake switch helps to detect when the brakes are being engaged, while the clutch switch governs the interaction between the engine and the transmission. The throttle switch controls air intake and fuel mixture, affecting engine performance. These components do not directly control the staged operation of the engine brake in the way that a faulty dash switch would, making it less likely for them to be the cause of limited engine braking engagement.