Component Tests and General Diagnostics

1. Disconnect vacuum hose from air switching/relief valve and connect a vacuum gauge to hose.
2. Apply parking brake and observe gauge reading.
3. On Rear Wheel Drive Models.
a. With engine cold, engine vacuum should be present on gauge until engine coolant temperature and charge temperature switch reach their normal operating temperatures. Then vacuum should drop to zero. If there is no vacuum with engine cold, check vacuum supply, air switching solenoid, coolant switch and charge-temperature switch and wiring connections to computer. If they are satisfactory, the computer may be defective, preventing air switching from occurring.
b. To check computer, connect a voltmeter to light green wire on air switching solenoid. With engine at normal operating temperature, start engine. Voltage should be less than one volt. Allow oxygen sensor feedback air switching schedule to time out. This will allow catalyst to reach normal operating temperature before the computer begins fuel control. When the warm-up schedule is completed, the solenoid will deenergize and the voltmeter will read charging system voltage. If not replace the solenoid and repeat the procedure. If voltmeter indicates charging system voltage before the warm-up schedule is completed, replace the computer.
4. To check air switching valve, disconnect air supply hose from valve. Disconnect vacuum hose from valve and connect an external vacuum source to valve. Start engine, air should flow from side port. Apply vacuum to valve. Air should flow from bottom port.