How does the transmission vacuum modulator valve work?
How does the transmission vacuum modulator valve work? by Greg Day. The transmission vacuum modulator valve determines how much load is on the engine so the transmission can shift properly. It has a vacuum line that connects to the intake and measures the amount of vacuum in the engine. How can you tell if your vacuum modulator is defective? The vacuum modulator measures the amount of this load so that the engine knows how hard to work to sustain the demand being placed on it. Most modern vehicles have a vacuum modulator in them. If your vacuum modulator were to...