GM Corvette 1984-1996 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 or exhaust pipe 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.



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Fig. Fig. 1: Typical oxygen sensor used on an early model vehicle



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Fig. Fig. 2: Later model vehicles use one or more heated oxygen sensors

Some vehicles are equipped with more than one 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 sensors signals until the sensor reaches about 600°F (316°C).
  6.  

TESTING



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. Check the O2S sensor voltage between the terminal and ground. Voltage should be between 350-500 millivolts. If the voltage doesnt fall within this range, the sensor is faulty.
  4.  



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Fig. Fig. 3: Oxygen sensor circuit-1988 vehicle shown, other years similar

  1. If the voltage is within specifications, recheck the voltage after starting the engine and running until it reaches normal operating temperature. With the engine running at 1200 rpm, then voltage should vary rapidly between 100-900 millivolts. If the voltage is not varying or not within the range, the sensor is faulty.
  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
vin J engines

See Figure 4

  1. Disconnect the 02 sensor connector and install jumper wires from the sensor connector to the wiring harness.
  2.  
  3. Start the engine and allow it to reach operating temperature. This should take about ten minutes. Turn the engine
  4.  

OFF.



  1. Connect the positive lead of a multimeter to the 02 sensor signal wire and the negative lead to the engine ground. Re-start the engine.
  2.  



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Fig. Fig. 4: Heated oxygen sensor circuit-VIN J engine

  1. The voltage reading should be fluctuating rapidly as the 02 sensor detects varying levels of oxygen in the exhaust stream.
  2.  
  3. If the 02 sensor voltage does not fluctuate, the sensor may be defective or mixture could be extremely out of range.
  4.  
  5. If the 02 sensor reads above 550 millivolts constantly, the fuel mixture is probably too rich. If the (02) sensor voltage reads below 350 millivolts constantly, the fuel mixture may be too lean or you may have an exhaust leak near the sensor.
  6.  
  7. Under normal conditions the 02 sensor should fluctuate high and low. Prior to condemning the 02 sensor, try forcing the system rich by restricting the air intake or lean by removing a vacuum line. If this causes the oxygen sensor to momentarily respond, look for problems in other areas of the system.
  8.  

VIN P AND 5 Engines
  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. 5: Heated Oxygen Sensor (HO2S) sensor circuit-VIN P and 5 engines

  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 doesnt 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 rapidly 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 6, 7 and 8


WARNING
The sensors use 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 proper operation of the oxygen 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 sensor may be difficult to remove when the engine temperature is below 120°F (48°C). Excessive removal force may damage the threads in the exhaust manifold or pipe; follow the removal procedure carefully.

  1. Make sure the ignition is OFF , then disconnect the negative battery cable.
  2.  
  3. Locate the oxygen sensor. It protrudes from the exhaust manifold or exhaust pipe (it looks somewhat like a spark plug). It may be necessary to raise and safely support the vehicle to access the sensor.
  4.  
  5. Unplug the sensor electrical connector.
  6.  



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Fig. Fig. 6: Typical oxygen sensor location and mounting-1990 VIN 8 shown



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Fig. Fig. 7: Some vehicles, such as this 1990 VIN J, use a left and right bank oxygen sensor-left shown, right similar



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Fig. Fig. 8: Later model vehicles equipped with heated oxygen sensors may have 2 sensors on each bank

There are special wrenches, either socket or open-end available from reputable retail outlets for removing the oxygen sensor. These tools make the job much easier and often prevent unnecessary damage.

  1. Carefully unscrew the sensor, then remove the oxygen sensor from the manifold or pipe.
  2.  

To install:
  1. During and after the removal, be very careful to protect the tip of the sensor if it is to be reused. Do not let it to come in contact with fluids or dirt. Do not clean it or wash it.
  2.  
  3. Apply a coat of anti-seize compound to the bolt threads but DO NOT allow any to get on the tip of the sensor.
  4.  
  5. Install the sensor in the manifold or exhaust pipe. Tighten the sensor to 30 ft. lbs. (41 Nm) for VIN 8, P or 5 engines, or to 42 ft. lbs. (55 Nm) for VIN J engines.
  6.  
  7. Attach the electrical connector and ensure a clean, tight connection.
  8.  
  9. If raised, carefully lower the vehicle.
  10.  
  11. Connect the negative battery cable.
  12.  

 
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