Mazda Trucks 1987-1993 Repair Guide

Oxygen Sensor

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OPERATION



The oxygen sensor supplies the computer with a signal which indicates a rich or lean condition during engine operation. The input information assists the computer in determining the proper air/fuel ratio. A low voltage signal from the sensor indicates too much oxygen in the exhaust (lean condition) and, conversely, a high voltage signal indicates too little oxygen in the exhaust (rich condition).

The oxygen sensors are threaded into the exhaust manifold and/or exhaust pipes on all vehicles. Heated oxygen sensors are used on some models to allow the engine to reach the closed loop faster.

TESTING



Heated Sensor

WARNING
Do not pierce the wires when testing this sensor; this can lead to wiring harness damage. Back probe the connector to properly read the voltage of the HO2S.

  1. Disconnect the HO2S.
  2.  
  3. Measure the resistance between PWR and GND terminals of the sensor. If the reading is approximately 6 ohms at 68°F (20°C). the sensor's heater element is in good condition.
  4.  
  5. With the HO2S connected and engine running, measure the voltage with a Digital Volt-Ohmmeter (DVOM) between terminals HO2S and SIG RTN (GND) of the oxygen sensor connector. If the voltage readings are swinging rapidly between 0.01-1.1 volts, the sensor is probably okay.
  6.  

Non-Heated Sensor

See Figure 1


WARNING
Do not pierce the wires when testing this sensor; this can lead to wiring harness damage. Back probe the connector to properly read the voltage of the O2S.

  1. Warm up the engine and allow it to run at idle.
  2.  
  3. Disconnect the O2S.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Inspection of the O2S terminal voltage

  1. Connect a voltmeter between the O2S and a good ground.
  2.  
  3. Run the engine at 4,500 rpm until the voltmeter reading indicates approximately 0.7V.
  4.  
  5. Increase and decrease the engine speed suddenly several times. Check to see that when the speed is increased, the voltmeter reads between 0.5V-1.0V and when the speed is decreased, the reading is between 0V-0.4V.
  6.  
  7. If the actual readings are out of specifications, replace the O2S.
  8.  

REMOVAL & INSTALLATION



See Figures 2 and 3

  1. Disconnect the negative battery cable.
  2.  
  3. Raise and safely support the vehicle on jackstands.
  4.  



Click image to see an enlarged view

Fig. Fig. 2: From underneath, locate the oxygen sensor (arrow), which is screwed into an exhaust component

  1. Disconnect the oxygen sensor from the engine control sensor wiring.
  2.  

If excessive force is needed to remove the sensors, lubricate the sensor with penetrating oil prior to removal.

Click image to see an enlarged view

Fig. Fig. 3: Using the proper wrench, loosen the oxygen sensor. Ensure that the wire and connector are unplugged

  1. Unscrew the sensor.
  2.  

To install:
  1. Install the sensor in the mounting boss, then tighten it to 27-33 ft. lbs. (37-45 Nm).
  2.  
  3. Reattach the sensor electrical wiring connector to the engine wiring harness.
  4.  
  5. Lower the vehicle.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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