1981 Mercedes Benz 280EFACTORY OEM SERVICE PROCEDURE

280 Models

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. If system does not operate after these checks, inspect belt tension and air pump operation. Remove test equipment and reinstall diagnostic connector cap.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.