Saturn Coupes/Sedans/Wagons 1991-1998 Repair Guide

Oxygen Sensor

Print

OPERATION



This sensor is used to report the concentration of oxygen in the exhaust. It consists of an arrangement of platinum and zirconia plates, all protected with a slotted outer shield. At about 600°F (318°C), the presence of oxygen in the exhaust will cause voltage to be generated across the dissimilar metals, up to a maximum of just under one volt. The PCM reads this signal and adjusts the fuel injector pulse width to maintain the right amount of oxygen in the exhaust for the catalytic converter to work properly. To quickly reach and stay at operating temperature, the sensor is threaded directly into the exhaust manifold. The threads are coated with an anti-seize compound. When replacing the sensor, be careful not to get anti-seize compound in the slots of the outer shield.

TESTING



See Figure 1

The only way to properly test just the oxygen sensor and circuit is with a scan tool connected to the ALDL. If an exhaust gas analyzer is available, a faulty sensor can be found if the rest of the fuel injection system works properly, and the sensor sends the PCM a message of too lean or too rich. Information about the sensor and engine operation can also be gained by running the engine in the Field Service Mode, described later in this guide.

  1. Using an ohmmeter, check the resistance of the oxygen sensor circuit to ground. Detach the connector for the purple wire from the oxygen sensor and read the wire resistance to ground; it should be at least 200 ohms.
  2.  
  3. With a scan tool connected, run the engine to normal operating temperature and follow the tool's menu to read oxygen sensor voltage. Sensor output should vary from approximately 350-550 millivolts.
  4.  
  5. Stop the engine and disconnect the sensor wire. With the wire from the PCM grounded and the ignition switch ON , the scan tool should show less than 100 millivolts. If not, the wiring or the PCM is faulty.
  6.  
  7. To test with an exhaust gas analyzer:
    1. No other faults can exist.
    2.  
    3. Run the engine at normal operating temperature for more than one minute.
    4.  
    5. The TPS must read more than 6.5 percent throttle opening.
    6.  

  8.  
  9. When the above conditions are met and all other engine systems work properly, the exhaust analyzer will change when the sensor wire is disconnected to simulate Open Loop Mode.
  10.  



Click image to see an enlarged view

Fig. Fig. 1: Schematic for the oxygen sensor circuit

REMOVAL & INSTALLATION



See Figures 2, 3 and 4

The oxygen sensor uses a permanently attached pigtail and connector, removal of which may affect the proper operation of the sensor.

  1. As an added safety precaution, you may wish to disable the air bag(s), if equipped. refer to Chassis Electrical for disabling procedure.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Unplug the sensor electrical connector.
  6.  
  7. Using a 19mm, 6-point crow's foot wrench, loosen and remove the oxygen sensor from the exhaust manifold.
  8.  

To install:

Be careful not to drop or damage the oxygen sensor when handling. The pigtail, connector and louvered end should be kept free of dirt or contaminants, but avoid using a solvent to clean the sensor.

  1. Coat the oxygen sensor threads with a nickel based anti-seize compound that does not contain silicone.
  2.  
  3. Install the oxygen sensor into the exhaust manifold and tighten to 18 ft. lbs. (25 Nm).
  4.  
  5. Attach the sensor electrical connector and install the Connector Position Assurance (CPA).
  6.  
  7. Connect the negative battery cable.
  8.  
  9. If necessary, enable the air bag(s). refer to Chassis Electrical .
  10.  



Click image to see an enlarged view

Fig. Fig. 2: Unplug the oxygen sensor connector



Click image to see an enlarged view

Fig. Fig. 3: Using a 19mm, 6-point crow's foot wrench, loosen the oxygen sensor



Click image to see an enlarged view

Fig. Fig. 4: Pull the oxygen sensor out of the exhaust manifold

 
label.common.footer.alt.autozoneLogo