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Home >> Mercedes Benz >> 1987 >> 560SL >> Repair and Diagnosis >> Engine Performance >> System >> Air Injection System >> Testing >> System Check
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System Check

  1. With engine at operating temperature, disconnect coolant temperature sensor plug and attach a 2.5-ohm test resistor to simulate +68°F (+20°C). Disconnect vacuum line from side connection of switchover valve and connect vacuum tester with "Y" fitting. Start engine. Disconnect suction hose to air pump at air filter and close with finger.
  2. Air pump should be running and vacuum present (about 20 in. Hg). Suction should be felt at end of hose to air pump. If okay, go to next step. If not okay, go to step 4).
  3. Air pump should disengage approximately 60 seconds and vacuum must drop to zero. If it does, system okay. If not, unplug injection relay. Vacuum should drop. If okay, replace air injection relay. If not okay, check routing of vacuum lines and/or switchover valve.
  4. Unplug air injection relay. Check voltage between terminals No. 4 and 5 at plug. Voltage should be about 12 volts. If not okay, check power supply and ground wiring. Check air shutoff valve function and air hoses for proper routing. If okay, go to next step.
  5. Check voltage between terminals No. 3 and 1 at plug. Voltage should be about 12 volts. If okay, replace air injection relay. If not okay, check power supply.
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