1987 Mercedes Benz 560SECFACTORY OEM SERVICE PROCEDURE

EGR System

  1. Apply about 12 in. Hg of vacuum to EGR valve. Disconnect vacuum line. The EGR valve should close. If not okay, replace EGR valve. If okay, go to step 2).
  2. Run engine at idle speed. Apply about 12 in. Hg of vacuum to EGR valve. Engine should run rough at idle. If not okay, replace EGR valve. If okay, go to step 3).
  3. Connect vacuum tester to EGR vacuum line using a "Y" fitting. Increase engine speed slowly to about 2500 RPM. Tester should indicate vacuum. If okay, test is complete. If not okay, go to step 4).
  4. Disconnect vacuum line from thermo valve and connect vacuum tester with "Y" fitting to vacuum line and thermo valve. Increase engine speed slowly to about 2500 RPM. Tester should indicate vacuum. If okay, replace vacuum control valve. If not okay, go to step 5).
  5. Disconnect both vacuum lines from thermo valve. Connect vacuum tester to angular connection of thermo valve and apply vacuum. With engine at operating temperature, thermo valve should be open. If not okay, replace thermo valve. If okay, go to step 6).
  6. Check for vacuum at line from throttle valve housing. There should be no vacuum at idle. If throttle valve is opened (at about 1500 RPM) vacuum should be present. If okay, test is complete. If not okay, correct connection of vacuum lines.
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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.