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Checking HO2S Heating Circuit

Location of Heated Oxygen (HO2S) sensor and harness connection. See COMPONENT LOCATIONS .

  1. Disconnect HO2S heater harness connector. See Figure. Connect DVOM between terminals No. 1 and 2 of HO2S heater harness connector, using adapter cables from connector test kit (VW 1594). See Figure. Start engine and let idle. Voltage must be 12-14 volts.
  2. If voltage is incorrect:
    • Check HO2S circuit breaker S73 in auxiliary relay panel 2, right A-pillar.
    • Check continuity between terminal No. 2 and HO2S circuit breaker S73. Resistance must be 0.5 ohm maximum (if necessary, check terminal number assignments). See WIRING DIAGRAMS .
    • Check continuity between terminal No. 1 and engine ground. Resistance must be 0.5 ohm maximum.
    • Check continuity (according to wiring diagram) between HO2S circuit breaker S73 and terminal No. 30 of fuel pump relay J17 (relay location 6). See Figure. Resistance must be 0.5 ohm maximum. See WIRING DIAGRAMS .
  3. If circuit is open, perform necessary repairs. If circuit is NOT open, switch DVOM to 10-Amp (DC) measuring range. Connect additional test cable (VW 1315 A/1) to harness connector position 2.
    4. NOTE: Current decreases as sensor temperature increases.
  4. Start engine and let idle. Must be 0.5-3.0 amps. If specified value is NOT obtained, replace HO2S sensor.
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