B4000 SE Cab Plus 4WD V6-4.0L OHV (1997)
Vacuum Brake Booster Check Valve: Testing and Inspection
1. Remove the clamps from the intake manifold or throttle body.
2. Apply suction and pressure to the hose from the engine side. Verify that air flows only toward the engine. If the air passes in both directions or not
at all, replace the check valve.