280 Models
- Warm engine to normal operating temperature. Remove cap from diagnostic connector on fenderwell. Connect the negative lead of a voltmeter to pin 3 in connector, and positive lead to battery voltage. Disconnect oxygen sensor connector. Voltmeter reading should be constant. Make a mark on voltmeter dial to indicate needle position.
- Connect oxygen sensor lead. Disconnect Purple/Blue hose at air duct housing and seal end of hose with finger. If voltage reading increases, system is operating properly. If not, continue with testing procedure.
- Check vacuum hose routing and ensure that hoses are tightly connected and no lines are plugged. Disconnect "Y" fitting at thermal vacuum valves and check for vacuum at "Y". If not present, clean intake manifold vacuum fitting.
- Check to ensure that air passes through both thermal vacuum valves. If not, replace closed valve. If both valves are open and pass air, replace diverter valve.
- If system does not operate after these checks, inspect belt tension and air pump operation. Remove test equipment and reinstall diagnostic connector cap.