LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Mercedes Benz >> 1991 >> 560SEC >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Emission Systems & Sub-Systems >> Air Injection
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Air Injection

  1. With engine off and at operating temperature, disconnect coolant temperature sensor connector. Install 2500-ohm test resistor between connector terminals No. 2 and 4, this step is to simulate 68°F (20°C) to CIS-E control unit. Disconnect vacuum line from side connection of switchover valve and connect vacuum tester in line using "Y" fitting.
  2. Start engine. Disconnect air suction hose at air pump filter and close off with finger. Air pump should be running and vacuum should be about 20 in. Hg. If suction is felt at end of hose, go to next step. If no suction is felt, go to step 4).
  3. The air pump must disengage after about one minute and the vacuum will drop to zero. If this does not happen, unplug air injection relay. If vacuum now drops, replace air injection relay. If vacuum still does not drop, check routing of vacuum lines and switchover valve. Repair or replace components as necessary.
  4. Unplug air injection relay. Check voltage between terminals No. 1 and 3 at plug connector. 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 connector. Voltage should be 12 volts. If voltage is incorrect, check power supply. If voltage is correct, replace air injection relay.
scientia non olet · About LEMON Manuals