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Home >> Mercedes Benz >> 1986 >> 560SL >> Repair and Diagnosis >> Engine Performance >> System >> Cis-E System >> Diagnostic Testing >> Test 9 >> Test On-Off Ratio
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Test On-Off Ratio

NOTE: If on-off ratio is 100% and idle speed is too high, check fuse on overvoltage protection relay and/or power supply and engine ground connection.
  1. On-off ratio cannot be adjusted. If on-off ratio tester needle oscillates, go to step 2). If okay, test is complete.
  2. Disconnect oxygen sensor plug and connect male part of plug to ground. Start engine and test sensor voltage between female part of plug and ground. Sensor voltage should be above 450 mV. If not okay, replace oxygen sensor. If not okay, go to step 3).
  3. Stop engine. Check wire from oxygen sensor plug to CIS-E control unit (terminal No. 8) for continuity. Resistance should be about zero ohms. If not okay, repair interruption. If okay, go to step 4).
  4. Loosen plug of oxygen sensor heater so that voltage can be measured at the pins (DO NOT disconnect plug). Pull off fuel pump relay and bridge terminals No. 7 and 8. Reading should be about 12 volts. If not okay, repair interruption. If okay, go to step 5).
  5. Unplug oxygen sensor heater plug. Connect Test Cable (102 589 04 63 00) with Adapter Plug (903 589 03 63 00). Measure current draw. Nominal value should be above .5 amps. If not okay, replace oxygen sensor. If okay, test is complete.
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