Vacuum System Check

Before testing, ensure fuses for cruise control system are OK and brake lights are operational. Check wiring between control unit wiring harness and component before assuming component is faulty. If electrical measurements are required, use multimeter tool No. US 1119, or equivalent.
1. Disconnect vacuum hose from vacuum pump, then depress servo unit diaphragm.
2. Plug disconnected vacuum hose. Diaphragm must remain in depressed state, without moving.
3. If diaphragm returns, check vent valves, servo unit or vacuum hoses for leaks, then repair as needed.
4. If diaphragm remains depressed, vacuum system is satisfactory.