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System Diagnosis

  1. Perform ON-BOARD DIAGNOSTIC (ODB) SYSTEM CHECK in the BASIC TESTING article. After performing OBD system check, go to next step.
  2. If DTC is present, diagnose DTC first. See the TESTS W/CODES article. If DTC is not present, go to next step.
  3. Visually inspect system. Check for disconnected or damaged vacuum hoses and components. Check linkage between vacuum actuators and valves for binding or interference with hoses. Ensure wiring is routed properly and not damaged. If problem is not found, go to next step. If problem is found, repair as necessary, then go to step 9).
  4. Connect scan tool to vehicle. Start engine and observe vacuum actuator linkages to switchover valves. Using scan tool, command each valve on and off. If both valves operate, go to next step. If both valves did not operate, go to step 6).
  5. Turn ignition off. Remove duct from between intake resonance switchover valve and throttle body. Hold throttle blades open to view moveable divider in back of intake manifold. Move actuator linkage by hand and ensure divider moves with linkage. Look down passages in intake resonance switchover valve to view moveable divider between 2 sides of valve. Move actuator linkage by hand to ensure divider moves with linkage. If both valves operate properly, system is okay. If one valve does not operate, go to next step. If both valves do not operate properly, replace affected valve/actuator assembly as necessary, then go to step 9).
  6. Using scan tool, exit device control. Disconnect manifold vacuum supply hose at solenoid valve while observing actuator linkage. If actuator does not move when vacuum is disconnected, go to next step. If actuator moves when vacuum is disconnected, replace solenoid valve, then go to step 9).
  7. Check for vacuum at manifold vacuum supply hose. If vacuum is present, go to next step. If vacuum is not present, repair vacuum supply hose or plugged vacuum source. Repair as necessary, then go to step 9).
  8. Disconnect other hose from solenoid valve and connect hoses together using suitable vacuum connector. If actuator linkage operates, replace solenoid valve, then go to next step. If actuator linkage does not operate, disconnect vacuum hose from actuator. If vacuum is present, replace valve/actuator assembly, then go to next step. If vacuum is not present, repair vacuum hose to actuator, then go to next step.
  9. Start engine. Observe vacuum actuator linkages for switchover valves. Using scan tool, command each valve on and off. If both valves operate, system is okay. If both valves do not operate, go to step 2).
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