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Oxygen Sensor Heater (Prizm GSi)

  1. Turn ignition on. Using voltmeter, check for battery voltage on Black/Red wire at oxygen sensor. If battery voltage exists, go to step 3).
  2. If battery voltage does not exist, check for open circuit in Black/Red wire between oxygen sensor and EFI main relay. EFI main relay is located in fuse/relay block on left front side of engine compartment.
  3. Start engine. Using voltmeter, check for varying voltage at Black/Red wire at oxygen sensor. Voltage should vary from one volt to battery voltage. If voltage does not vary, check resistance of oxygen sensor heater using ohmmeter.
  4. Resistance should be about 3.5-14.0 ohms. Resistance will vary with temperature. If resistance is okay, check wiring to ECM. See appropriate wiring diagram in WIRING DIAGRAMS article in this section. The ECM is located in center of instrument panel, behind console. If wiring is okay, replace ECM.
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