GM Corsica/Beretta 1988-1996 Repair Guide

Oxygen Sensor

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OPERATION



See Figures 1 and 2

There are two types of oxygen sensors used in these vehicles. They are the single wire oxygen sensors (O2S) and the heated oxygen sensor (HO2S). The oxygen sensor is a spark plug shaped device that is threaded into the exhaust manifold and protrudes into the exhaust stream which monitors the oxygen content of the exhaust gases. The difference between the oxygen content of the exhaust gases and that of the outside air generates a voltage signal that is sent to the computer control module. The control module monitors this voltage and, depending upon the value of the signal received, issues a command to adjust for a rich or a lean condition.

Some vehicles are equipped with more than one heated oxygen sensor.



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Fig. Fig. 1: Cross-sectional view of a single-wire oxygen sensor



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Fig. Fig. 2: Cutaway view of a heated oxygen sensor

No attempt should ever be made to measure the voltage output of the sensor. The current drain of any conventional voltmeter would be such that it would permanently damage the sensor.

The proper operation of the oxygen sensor depends upon three basic conditions:

  1. Good electrical connections. Since the sensor generates low currents, good clean electrical connections at the sensor are a must.
  2.  
  3. Outside air supply. Air must circulate to the internal portion of the sensor. When servicing the sensor, do not restrict the air passages.
  4.  
  5. Proper operating temperatures. The computer control module will not recognize the sensor's signals until the sensor reaches about 600°F (316°C).
  6.  

TESTING



Single Wire Oxygen Sensor (O2S)

See Figure 3

  1. Perform a visual inspection of the connector, making sure it is engaged properly and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. Start the engine and run until the engine reaches normal operating temperatures (closed loop, or coolant temperature at 167-203°F.
  4.  
  5. Detach the oxygen sensor connector, then connect a voltmeter to the terminal and a known engine ground.
  6.  



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Fig. Fig. 3: Oxygen Sensor (HO2S) sensor circuit

  1. Check the voltage with the engine running above 1200 rpm:
    1. If the voltage is fluctuating between 0.1-1.0 volts (100-999 mV), the system is operating normally.
    2.  
    3. If the voltage does not fluctuate as specified, replace the sensor.
    4.  
    5. If the voltage is below 0.35 volts (350 mV), a lean condition exists.
    6.  
    7. If the voltage is above 0.75 volts (750 mV), a rich condition exists.
    8.  

  2.  
  3. If the voltage is within specifications, check the circuits back to the PCM for continuity.
  4.  
  5. If the sensor and circuits are functioning properly, the PCM may be faulty.
  6.  

Heated Oxygen Sensor (HO2S)

See Figure 4

  1. Visually check the connector, making sure it is engaged properly and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. Detach the sensor electrical connector and check resistance between terminals C and D. Resistance should be 10-15 ohms at 70°F. If resistance is not within specifications, the sensor heater is faulty.
  4.  
  5. If resistance is within specification, check for battery positive (B+) between connector terminals C and D with the ignition ON . If battery positive (B+) is not present, check the circuit continuity back to the PCM. If the circuits are functioning properly, the PCM may be faulty.
  6.  



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Fig. Fig. 4: Heated Oxygen Sensor (HO2S) sensor circuit

  1. Check the HO2S sensor voltage between terminals A and B with the engine OFF . The voltage should be between 350-500 millivolts. If the voltage doesn't fall within that range, the sensor is faulty.
  2.  
  3. If the voltage is within specifications, recheck the voltage after heating the engine to normal operating temperature. With the engine running at 1200 rpm, then voltage should vary between 100-900 millivolts. If the voltage is not varying or not within the range, the sensor is faulty.
  4.  
  5. If the voltage is within specifications, check the circuits back to the PCM for continuity.
  6.  
  7. If the sensor and circuits are functioning properly, the PCM may be faulty.
  8.  

REMOVAL & INSTALLATION



See Figures 5, 6 and 7

The oxygen sensor may be difficult to remove when the engine temperature is below 120°F (49°C). Excessive removal force may damage the threads in the exhaust manifold or pipe; follow the removal procedure carefully.

  1. Locate the oxygen sensor. It may protrudes from the center of the exhaust manifold at the front of the engine compartment (it looks somewhat like a spark plug) or be located along the exhaust pipe.
  2.  



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Fig. Fig. 5: Some vehicles may have an oxygen sensor (see arrow) mounted along the exhaust pipe

  1. If necessary for access to the sensor, remove the exhaust manifold head shield or raise and safely support the vehicle, as necessary.
  2.  
  3. Detach the electrical connector from the oxygen sensor.
  4.  
  5. Spray a commercial heat riser solvent onto the sensor threads and allow it to soak in for at least five minutes.
  6.  
  7. Carefully unscrew and remove the sensor from the vehicle.
  8.  



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Fig. Fig. 6: Using an open-ended wrench may make removal of the oxygen sensor easier



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Fig. Fig. 7: When removing the O2 sensor, be careful not to damage the electrical connector - 1995 2.2L (VIN 4) engine shown

To install:

A special anti-seize compound is used on the oxygen sensor threads. The compound consists of a liquid graphite and glass beads. The graphite will burn away, but the glass beads will remain, making the sensor easier to remove.

  1. Coat the new sensor's threads with GM anti-seize compound No. 5613695 or the equivalent. This is not a conventional anti-seize paste. The use of a regular compound may electrically insulate the sensor, rendering it inoperative. You must coat the threads with an electrically conductive anti-seize compound.
  2.  

New or service sensors will already have the compound applied to the threads. If a sensor is removed from the engine, and for any reason it is to be reinstalled, the threads must have anti-seize compound applied before reinstallation.

  1. Install the sensor and tighten to 28-33 ft. lbs. (42 Nm.). Do not overtighten.
  2.  
  3. Attach the electrical connector. Be careful not to damage the electrical pigtail. Check the sensor boot for proper fit and installation.
  4.  
  5. If removed, install the exhaust manifold heat shield.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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