Mazda 323/MX-3/626/MX-6/Millenia/Protégé 1990-1998 and Ford Probe 1993-1997

Oxygen Sensor

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OPERATION



See Figure 1

The oxygen sensor reacts with the oxygen in the exhaust gases and sends a voltage signal to the ECU based on this reaction. A low voltage signal indicates too much oxygen or a lean condition while a high voltage signal indicates not enough oxygen or a rich condition. The ECU uses this information along with other sensor inputs to calculate air/fuel ratio.



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Fig. Fig. 1: The O2 sensor (A) is threaded into the exhaust so that the element (B) is in the exhaust gas stream

The oxygen sensor is threaded into the exhaust manifold and/or pipes on all engines except turbocharged engines. On turbocharged engines, the sensor is screwed into the turbocharger itself.

Some Mazda engines utilize more than one oxygen sensor, often having a front and rear sensor (as in V6 engines) and/or pre- and post catalytic converter sensors (which enables the ECU to measure catalytic converter efficiency).

TESTING



Sensor Output Voltage

See Figures 2, 3 and 4

If equipped with a heated element oxygen sensor (more than one wire connection), perform the Heater Element Resistance test first, as it requires a specific temperature. Performing the output voltage test first will require you to wait for the engine to almost completely cool down.

  1. Start the engine and bring to normal operating temperature.
  2.  
  3. Detach the oxygen sensor connector.
  4.  



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Fig. Fig. 2: Measure the single wire sensors by grounding one terminal of the voltmeter and reading the sensor terminal with the engine running



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Fig. Fig. 3: Oxygen sensor terminal identification for 3-wire sensors. If only one three wire sensor is used, the FRONT (LH) diagram should be used



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Fig. Fig. 4: Oxygen sensor connections for the 4-wire sensors

  1. On single wire connectors, measure the voltage between the oxygen sensor wire and ground.
  2.  
  3. On three wire connectors, measure the voltage between the oxygen sensor wire terminal A and ground.
  4.  
  5. On four wire connectors, measure the voltage between the oxygen sensor wire terminal A and terminal B.
  6.  
  7. When the engine speed is increased, the voltage should be 0.5-1.0 volts. When decreasing engine speed, the voltage should drop to 0-0.4 volts.
  8.  

Voltage that remains above 0.55 volts indicates a continuously rich condition while below 0.55 volts indicates a continuously lean condition. Rich or lean conditions could be an indication of another problem.

  1. If the voltage readings are not as specified, replace the oxygen sensor.
  2.  

Heater Element Resistance

See Figures 3 and 4

This procedure does not apply to single wire sensors.

  1. Detach the oxygen sensor connector.
  2.  
  3. On three wire connectors, measure the resistance between terminals B and C.
  4.  
  5. On four wire connectors, measure the resistance between terminals C and D.
  6.  
  7. On all sensors except four wire front sensors, the resistance should read approximately 6 ohms at 68°F (2°C).
  8.  
  9. On four wire front sensors, the resistance should read approximately 13 ohms at 68°F (2°C).
  10.  

If the sensor readings are out of range, double check the temperature of the sensor. If the temperature is too hot or cold, it may influence an inaccurate reading. If possible, adjust the temperature of the sensor to the proper specification and re-check it.

  1. If the readings are not within range, replace the oxygen sensor.
  2.  

REMOVAL AND INSTALLATION



Except Turbocharged Engines

See Figures 5, 6, 7 and 8

  1. If necessary, remove the under vehicle splash shield.
  2.  
  3. Detach the oxygen sensor electrical connector.
  4.  



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Fig. Fig. 5: To remove the oxygen sensor, first remove any splash shielding from the underside of the vehicle as required



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Fig. Fig. 6: Detach the oxygen sesnor wire connection ...



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Fig. Fig. 7: ... then loosen the sensor ...



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Fig. Fig. 8: ... and remove it from the exhaust pipe or manifold

  1. On some California models equipped with a V6 engine, it may be necessary to remove the exhaust manifold due to space limitations.
  2.  
  3. Remove the oxygen sensor from the exhaust manifold or pipe.
  4.  
  5. Installation is the reverse of the removal procedure. Tighten the oxygen sensor to 4-36 ft. lbs. (29-49 Nm).
  6.  

Turbocharged Engines
  1. Disconnect the negative battery cable.
  2.  
  3. Detach the sensor electrical connector.
  4.  
  5. Remove the wiring harness from the spark plug wire retaining bracket and the retaining bracket on the turbocharger heat shield.
  6.  
  7. Remove the sensor from the turbocharger.
  8.  
  9. Installation is the reverse of the removal procedure.
  10.  

 
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