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Home >> Mercedes Benz >> 1990 >> 560SEC >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Emission Systems & Sub-Systems >> Air Injection Test
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Air Injection Test

  1. With engine at operating temperature, disconnect coolant temperature sensor. Connect 2500-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.
  2. Start engine. Disconnect suction hose at air pump filter and close with finger. Air pump should be running and vacuum should be about 20 in. Hg. Suction should be felt at end of hose to air pump. If no suction is felt, go to step 4). If okay, go to next step.
  3. The air pump must disengage after about one minute and the vacuum will drop to zero. If not okay, unplug air injection relay. If vacuum drops, replace air injection relay. If vacuum doesn't drop, check routing of vacuum lines and switchover valve. Repair or replace components as necessary.
  4. Unplug air injection relay. Check voltage between terminal Nos. 1 and 3 at plug. Voltage should be about 12 volts. If voltage is not about 12 volts, check power supply and ground wiring. Check air shutoff valve function and air hoses for proper routing.
  5. Check voltage between terminal No. 1 and terminal No. 2 at plug. Voltage should be 12 volts. If voltage is incorrect, check power supply. If okay, replace air injection relay.
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