Mazda B-Series 1998-06

Heated 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).



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Fig. Typical Heated Oxygen Sensor (H2OS)-most vehicles are equipped with multiple sensors

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

The oxygen sensor supplies the computer with a signal that 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).

Removal & Installation



1994-95 MPV models equipped with the 2.6L engine use 1 Oxygen Sensor (O2S). 1994-95 MPV models equipped with the 3.0L engine use 1 Heated Oxygen Sensor (HO2S). These sensors are located on the exhaust pipe between the exhaust manifold and the catalytic converter. 1996-98 MPV models use 2 HO2 sensors. V6 equipped B Series Pick-up models use three HO2S's, and 2.3L engines use two HO2S's for the engine control system. The heated sensors are located before and after the dual converters in the exhaust pipes. On 1994-95 V6 engines, there are two sensors, one is located in the left exhaust manifold and the other in the dual converter Y-pipe. 1994-95 2.3L engines use only one sensor.

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



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Fig.

  1. Disconnect the HO2S 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.



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

  1. Remove the sensors with a sensor removal tool, such as Ford Tool T94P-9472-A.
  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.  


CAUTION
The temperature of the exhaust system is extremely high after the engine has been run. To prevent personal injury, allow the exhaust system to cool completely before removing sensor from the exhaust system.

  1. Disconnect the negative battery cable.
  2.  
  3. Raise and safely support the vehicle on jack stands.
  4.  
  5. Disconnect the HO2S from the engine control sensor wiring.
    NOTE
    If excessive force is needed to remove the sensors lubricate the sensor with penetrating oil prior to removal.

  6.  
  7. Remove the sensors with a sensor removal tool, such as Ford Tool T94P-9472-A or equivalent.
  8.  

To install:

  1. Install the sensor in the mounting boss, and then tighten it to 27-33 ft. lbs.
  2.  
  3. Connect the sensor electrical wiring connector to the engine wiring harness.
  4.  
  5. Lower the vehicle.
  6.  
  7. Connect the negative battery cable.
  8.  

Testing




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.  

Heater Circuit
  1. Disconnect the HO2S connector.
  2.  
  3. Measure the resistance between the HO2S terminals C and D. Standard value:
    1. Front sensor-3.0-3.6 ohms
    2.  
    3. Rear sensor-5.0-7.0 ohms
    4.  

  4.  
  5. If not as specified, replace the HO2S.
  6.  
  7. If within specifications, check connectors and wiring between the sensor and ECM/PCM.
  8.  

Oxygen Sensor Circuit
  1. Warm up the engine and run it at idle.
  2.  
  3. Disconnect the HO2S connector.
  4.  
  5. Connect the voltmeter positive test lead terminal A and negative test lead to terminal B.
  6.  
  7. With the vehicle stopped, run the engine at 3,000 rpm until the voltmeter moves between 0.5 and 0.7 V.
  8.  
  9. Measurement the voltage changes when the engine speed increases and decreases suddenly several times. Standard value:
    1. Acceleration-0.5-1.0 volt
    2.  
    3. Deceleration-0-0.5 volt
    4.  

  10.  
  11. If not as specified, replace the HO2S.
  12.  
  13. If within specification, check wiring harness and connectors between HO2S and PCM.
  14.  

 
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