GM Lumina/Grand Prix/Cutlass Supreme/Regal 1988-1996

Oxygen Sensor

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OPERATION



There are two types of oxygen sensor's 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 received signal, issues a command to the mixture control solenoid on the carburetor to adjust for rich or lean conditions.

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 600ºF (316ºC).
  6.  
  7. Non-leaded fuel. The use of leaded gasoline will damage the sensor very quickly.
  8.  

Precautions:


Careful handling of the oxygen sensor is essential.
 
The electrical pigtail and connector are permanently attached and should not be removed from the oxygen sensor.
 
The inline electrical connector and louvered end of the oxygen sensor must be kept free of grease, dirt and other contaminants.
 
Avoid using cleaning solvents of any type on the oxygen sensor.
 
Do not drop or roughly handle the oxygen sensor.
 
The oxygen sensor may be difficult to remove if the engine temperature is below 120ºF (48ºC). Excessive force may damage the threads in the exhaust manifold or exhaust pipe.
 

TESTING



Single Wire Sensor

See Figures 1 and 2



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Fig. Fig. 1: Oxygen sensor (O2S) wiring diagram, except 2.5L engine



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Fig. Fig. 2: Oxygen sensor (O2S) wiring diagram-2.5L engine

  1. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
  2.  
  3. Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (02S) and battery ground.
  4.  
  5. Verify that the O2S voltage fluctuates rapidly between 0.35-0.55 volts.
  6.  
  7. If the O2S voltage is stabilized at the middle of the specified range (approximately 0.40-0.50 volts) or if the 02S voltage fluctuates very slowly between the specified range (02S signal crosses 0.5 volts less than 5 times in ten seconds), the 02S may be faulty.
  8.  
  9. If the 02S voltage stabilizes at either end of the specified range, the ECM is probably not able to compensate for a mechanical problem such as a vacuum leak or a faulty pressure regulator. These types of mechanical problems will cause the 02S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the 02S test repeated.
  10.  
  11. Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a lean mixture condition. Reattach the vacuum hose.
  12.  
  13. Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a rich mixture condition.
  14.  
  15. If the 02S voltage is above or below the specified range, the 02S and/or the O2S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.
  16.  

Heated Oxygen Sensor

See Figures 3, 4, 5 and 6



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Fig. Fig. 3: Heated Oxygen Sensor (H02S) wiring diagram-1993 vehicles



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Fig. Fig. 4: Heated Oxygen Sensor (H02S) wiring diagram - 1994-96 3.1L engines



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Fig. Fig. 5: Heated Oxygen Sensor (H02S) wiring diagram - 1994-96 3.4L engine



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Fig. Fig. 6: Heated Oxygen Sensor (H02S) wiring diagram - 1994-96 3.8L engines

  1. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
  2.  
  3. Turn the ignition OFF , then disengage the H02S harness connector.
  4.  
  5. Connect a test light between harness terminals A and B. With the ignition switch ON and the engine OFF, verify that the test light is lit. If the test light is not lit, either the supply voltage to the H02S heater or the ground circuit of the H02S heater is faulty. Check the H02S wiring and the fuse.
  6.  
  7. Next, connect a high impedance ohmmeter between the H02S terminals B and A and verify that the resistance is 3.5-14.0 ohms.
  8.  
  9. If the H02S heater resistance is not as specified, the H02S may be faulty.
  10.  
  11. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
  12.  
  13. Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (02S) and battery ground.
  14.  
  15. Verify that the 02S voltage fluctuates rapidly between 0.35-0.55 volts.
  16.  
  17. If the 02S voltage is stabilized at the middle of the specified range (approximately 0.40-0.50 volts) or if the 02S voltage fluctuates very slowly between the specified range (02S signal crosses 0.5 volts less than 5 times in ten seconds), the 02S may be faulty.
  18.  
  19. If the 02S voltage stabilizes at either end of the specified range, the ECM is probably not able to compensate for a mechanical problem such as a vacuum leak or a faulty fuel pressure regulator. These types of mechanical problems will cause the 02S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the 02S test repeated.
  20.  
  21. Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a lean mixture condition. Reattach the vacuum hose.
  22.  
  23. Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a rich mixture condition.
  24.  
  25. If the 02S voltage is above or below the specified range, the 02S and/or the O2S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.
  26.  

REMOVAL & INSTALLATION



See Figures 7, 8, 9, 10, 11, 12 and 13

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Fig. Fig. 7: The oxygen sensor is threaded into the exhaust manifold-2.2L engine



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Fig. Fig. 8: View of the oxygen sensor mounting-2.3L engine



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Fig. Fig. 9: Oxygen sensor location-2.5L engine



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Fig. Fig. 10: Heated Oxygen Sensor (HO2S) location-1995 3.1L engine shown



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Fig. Fig. 11: Oxygen sensor location-3.4L engine shown



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Fig. Fig. 12: This 3.8L engine has one H02S mounted on the exhaust manifold...



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Fig. Fig. 13: ... and a second HO2S mounted after the catalytic converter


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!

The oxygen sensor may be difficult to remove when the temperature of the engine is below 120ºF (49ºC). Excessive force may damage the threads in the exhaust manifold or exhaust pipe.

  1. Disconnect the negative battery cable.
  2.  
  3. For 3.1L engines, unbolt the coolant recovery reservoir (do not disconnect the hoses) and position aside. Unfasten the engine torque strut bolt, then rotate the engine forward.
  4.  
  5. If necessary for access, raise and safely support the vehicle, remove the intermediate pipe and heat shield.
  6.  
  7. Unplug the electrical connector and any attaching hardware.
  8.  

Some late model vehicles utilize two oxygen sensors.

  1. Remove the sensor from the vehicle. For some vehicles, it may be necessary to use tool J 29533/BT-8127 or equivalent to remove the sensor.
  2.  

To install:
  1. Coat the threads of the sensor with a GM anti-seize compound, part number 5613695, or its equivalent, before installation. New sensors are pre-coated with this compound.
  2.  

The GM anti-seize compound is NOT a conventional anti-seize paste. The use of a regular paste may electrically insulate the sensor, rendering it useless. The threads MUST be coated with the proper electrically conductive anti-seize compound.

  1. Install the sensor and tighten to 30 ft. lbs. (40 Nm). Use care in making sure the silicone boot is in the correct position to avoid melting it during operation.
  2.  
  3. Engage the electrical connector.
  4.  
  5. If necessary, install the heat shield, attach the intermediate pipe, then carefully lower the vehicle.
  6.  
  7. On 3.1L engines, rotate the engine back to its original position, then install the torque strut bolt. Position and fasten the coolant recovery reservoir.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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