The O2 sensor must be tested with the engine in oprating temperature. Disconnect O2 sensor plug. O2 sensor pulg is located inside car, under floormat, near passenger seat. Disconnect O2 sensor plug and connect male part to ground. Start engine, test sensor voltage between female part of plug and ground. Sensor voltage must be above 450 mV. If not, replace O2 sensor. Test for continuity between male part of plug and ECU plug term #8. Repair interruption if necessary.
Test O2 sensor heater. Engine shut off. Loosen plug of O2 sensor to allow voltage testing. Pull off fuel pump relay and jump terminal 7&8. Reading, battery voltage, OK. Not battery voltage. Repair interruption. Unplug O2 sensor heater plug. Connect test cable 102 589 04 63 00) with adapter plug 903 589 03 63 00. Test current draw. Above 0.5A OK. End of test. Not OK, replace O2 sensor, repeat the procedure. You can make your own test cable from parts available at Radio Shack. Also if you decide to use other then MB oxygen sensor. Make sure it meets the MB spec.
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