GM Prizm/Nova 1985-1993 Repair Guide

Oxygen Sensor

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The oxygen (O 2 ) sensor is located on the exhaust manifold to detect the concentration of oxygen in the exhaust gas. Using highly refined metals (zirconia and platinum), the sensor uses changes in the oxygen content to generate an electrical signal which is transmitted to the ECM. The computer in turn reacts to the signal by adjusting the fuel metering at the injectors or at the carburetor. More or less fuel is delivered into the cylinders and the correct oxygen level is maintained.

TESTING



1985-88 VIN Code 4 Engine

See Figure 1

  1. Warm up the engine to normal operating temperature.
  2.  
  3. Connect the voltmeter to the service connector. This round, green connector is located behind the right shock tower. Connect the positive probe to the OX terminal and the negative probe to the E terminal.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Testing hook-up for the oxygen sensor - 1985-88 VIN code 4 engine

  1. Run the engine at 2500 rpm for 90 seconds or more. This allows the sensor to achieve a stable temperature and the exhaust flow to stabilize.
  2.  
  3. Maintain the engine at 2500 rpm and check the meter. The meter needle should fluctuate at least 8 times in 10 seconds in the 0-6 volt range. This indicates that the sensor is working properly.
  4.  
  5. If the sensor fails the test, perform a careful inspection of all the wiring and connectors in the system. A loose connection can cause the sensor to fail this test. Repeat the voltage test after the inspection.
  6.  

1988 VIN Code 5 Engine

See Figure 2

  1. Warm up the engine to normal operating temperature.
  2.  
  3. Connect the voltmeter to the check connector. Hook the negative probe to terminal VF and the positive probe to terminal E1 .
  4.  



Click image to see an enlarged view

Fig. Fig. 2: Testing hook-up for the oxygen sensor - 1988 VIN code 5 engine

  1. Run the engine at 2500 rpm for at least 90 seconds.
  2.  
  3. With the engine speed being maintained at 2500 rpm, use a jumper wire to connect terminals T and E1 at the check connector.
  4.  
  5. Watch the voltmeter and note the number of times the needle fluctuates in 10 seconds. If it moves 8 times or more, the sensor is working properly.
    1. If the needle moves less than 8 times but more than zero, disconnect the terminal T-to-E1 jumper. Still maintaining 2500 rpm, measure the voltage between terminals E1 and VF . If the voltage is above zero, replace the oxygen sensor. If the voltage is zero, read and record the diagnostic codes (refer to Check Engine Light and Diagnostic Codes later in this Section) and repair the necessary items.
    2.  
    3. If the needle does not move at all (zero), read and record the trouble codes and repair the affected system.
    4.  

  6.  

Perform a careful inspection of all the wiring and connectors in the system. A loose connection can cause the sensor to fail these tests. Repeat the voltage test after the inspection. (Refer to Check Engine Light and Diagnostic Codes later in this Section.)

1989-93 Engines

For oxygen sensor diagnostic testing on these engines, please refer the appropriate code charts at the end of this Section.

REMOVAL & INSTALLATION




WARNING
Care should be used during the removal of the oxygen sensor. Both the sensor and its wire can be easily damaged.

  1. The best condition in which to remove the sensor is with the engine in a mid-warm state. This is generally achieved after 2 to 5 minutes (depending on outside temperature) of running after a cold start. The exhaust manifold has developed enough heat to expand and make the removal easier but is not so hot that it has become untouchable.Wearing heat resistant gloves is highly recommended during this repair.
  2.  
  3. With the ignition OFF, disconnect the wiring for the sensor.
  4.  
  5. Unscrew the oxygen sensor from the manifold.
  6.  

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

  1. During and after the removal, use great care to protect the tip of the sensor if it is to be reused. Do not allow it to come in contact with fluids or dirt. Do not attempt to clean it or wash it.
  2.  
  3. When re-installing, apply a coat of anti-seize compound to the threads but DO NOT allow any to get on the tip of the sensor. This includes any accidental or momentary contact from rags, etc..
  4.  

Most replacement sensors come with the compound already on the threads. Do not remove it or try to clean it. On these sensors, application of anti-seize compound is not necessary.

  1. Install the sensor in the manifold. Tighten it to 30 ft. lbs.
  2.  
  3. Reconnect the electrical connector and insure a clean, tight connection.
  4.  

 
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