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.  



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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