GM Bonneville/Eighty Eight/LeSabre 1986-1999

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 Sensor (02S) and the Heated Oxygen Sensor (H02S). The oxygen sensor is a spark plug shaped device that is screwed into the exhaust manifold. It monitors the oxygen content of the exhaust gases and sends a voltage signal to the Electronic Control Module (ECM). The ECM monitors this voltage and, depending on the value of the signal received, issues a command to adjust for a rich or lean condition.



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Fig. Fig. 1: Early model vehicles use a single wire oxygen sensor



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Fig. Fig. 2: A heated oxygen sensor was implemented on later models

The heated oxygen sensor has a heating element incorporated into the sensor to aid in the warm up to the proper operating temperature and to maintain that temperature.

The proper operation of the oxygen sensor depends upon four 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 ECM will not recognize the sensor's signals until the sensor reaches approximately 600°F (316°C).
  6.  
  7. Non-leaded fuel. The use of leaded gasoline will damage the sensor very quickly.
  8.  

Precautions:
  1. Careful handling of the oxygen sensor is essential.
  2.  
  3. The electrical pigtail and connector are permanently attached and should not be removed from the oxygen sensor.
  4.  
  5. The in-line electrical connector and louvered end of the oxygen sensor must be kept free of grease, dirt and other contaminants.
  6.  
  7. Avoid using cleaning solvents of any type on the oxygen sensor.
  8.  
  9. Do not drop or roughly handle the oxygen sensor.
  10.  
  11. The oxygen sensor may be difficult to remove if the engine temperature is below 120°F (48°C). Excessive force may damage the threads in the exhaust manifold or exhaust pipe.
  12.  

TESTING



Single Wire Sensor
  1. Visually inspect the connector to be sure it is connected properly and all of the terminals are on straight, tighten and free of corrosion or other damage.
  2.  
  3. Check the oxygen sensor voltage between the terminals (on 2 wire sensors) of between the sensor terminal and ground (on 1 wire sensors). The voltage should be between 350-500 millivolts. If the voltage is outside of specifications, the sensor is faulty.
  4.  
  5. If the voltage is within specifications, recheck the voltage after heating the engine to normal operating temperature (closed loop status). With the engine running at about 1,200 rpm, the voltage should vary between 100-900 millivolts. If the voltage is not varying or is not within specifications, the sensor is faulty.
  6.  
  7. If the voltage is within specifications, check the circuits back to the ECM for continuity.
  8.  
  9. If the sensor and circuits are functional, the PCM may be bad.
  10.  

Heated Oxygen Sensor

See Figure 3

  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 79°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. 3: Schematic of a Heated Oxygen Sensor (HO2S) 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 4, 5, 6, 7 and 8


WARNING
The sensor uses a permanently attached pigtail and connector. This pigtail should not be removed from the sensor. Damage or removal of the pigtail or connector could affect the proper operation of the sensor. Keep the electrical connector and louvered end of the sensor clean and free of grease. NEVER use cleaning solvents of any type on the sensor!

  1. Disconnect the negative battery cable.
  2.  
  3. Locate the oxygen sensor. It protrudes from the center of the exhaust manifold at the front or rear of the engine compartment; (it looks somewhat like a spark plug).
  4.  
  5. If necessary, raise and safely support the vehicle for access to the oxygen sensor.
  6.  
  7. It may be necessary to tag and disconnect any spark plug wires that obstruct the oxygen sensor.
  8.  



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Fig. Fig. 4: This spark plug wire may have to be disconnected for access to the O2 sensor

  1. Detach the electrical connector from the oxygen sensor.
  2.  



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Fig. Fig. 5: Unplug the O2 sensor electrical connector

  1. Spray a commercial heat riser solvent onto the sensor threads and allow it to soak in for at least five minutes.
  2.  
  3. Carefully unscrew and remove the sensor. There are special sockets available that make oxygen sensor removal easier.
  4.  



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Fig. Fig. 6: There is a special socket that, along with a ratchet and extension ...



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Fig. Fig. 7: ... you can use to remove the O2 sensor from the manifold



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Fig. Fig. 8: Single wire oxygen sensor mounting - 1991 vehicle 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.  
  3. Install the sensor and tighten it to 30 ft. lbs. (8 Nm). Do not overtighten.
  4.  
  5. Attach the electrical connector. Be careful not to damage the electrical pigtail. Check the sensor boot for proper fit and installation.
  6.  
  7. If raised, carefully lower the vehicle.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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