Toyota Celica, Corolla, ECHO & MR2 1999-05

Oxygen Sensor

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Operation



The exhaust oxygen sensor or O 2 S, is mounted in the exhaust stream where it monitors oxygen content in the exhaust gas. The oxygen content in the exhaust is a measure of the air/fuel mixture going into the engine. The oxygen in the exhaust reacts with the oxygen sensor to produce a voltage which is read by the ECM.

There are two types of oxygen sensors used in these vehicles. They are the single wire oxygen sensor (O 2 S) and the heated oxygen sensor (HO 2 S). The oxygen sensor is a spark plug shaped device that is screwed into the exhaust manifold. It monitors the oxygen content of the exhaust gases and sends a voltage signal to the Electronic Control Module (ECM). The ECM monitors this voltage and, depending on the value of the received signal, issues a command to the mixture control solenoid on the throttle body to adjust for rich or lean conditions.

The heated oxygen sensor has a heating element incorporated into the sensor to aid in the warm up to the proper operating temperature and to maintain that temperature.

The proper operation of the oxygen sensor depends upon four basic conditions:



Good electrical connections. Since the sensor generates low currents, good clean electrical connections at the sensor are a must.
 
Outside air supply. Air must circulate to the internal portion of the sensor. When servicing the sensor, do NOT restrict the air passages.
 
Proper operating temperatures. The ECM will NOT recognize the sensor's signals until the sensor reaches approximately 600°F (316°C).
 
Non-leaded fuel. The use of leaded gasoline will damage the sensor very quickly.
 

Removal & Installation



The oxygen sensor can be located in several places. Either in the exhaust manifold, front pipe or catalytic converter.


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 when the engine is moderately warm. This is generally achieved after two to five 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.  



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Fig. Note the manifold mounted sensor is obtained through the heat shield

  1. With the ignition OFF , unplug the connector for the sensor.
  2.  



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Fig. Remove the wiring from the sensor located near the radiator

  1. Remove the two sensor attaching bolts.
  2.  



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Fig. One oxygen sensor is attached to the front exhaust pipe on all models



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Fig. Two nuts retain the O2 sensor on the exhaust manifold

  1. Remove the oxygen sensor from its mounting place and discard the gasket.
  2.  



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Fig. Extract the sensor from the manifold and ...



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Fig. ... the gasket

A special socket is available to remove the sensor.

To install:

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.

  1. Apply a coat of anti-seize compound to the bolt threads but DO NOT allow any to get on the tip of the sensor.
  2.  
  3. Position a new gasket, install and secure the sensor.
  4.  
  5. Reattach the electrical wiring and insure a clean, tight connection.
  6.  

Testing




WARNING
Do NOT pierce the wires when testing this sensor; this can lead to wiring harness damage. Backprobe the connector to properly read the voltage of the HO 2 S.

2.2L (5S-FE) VIN G
  1. Disconnect the oxygen sensor connector.
  2.  
  3. Using an ohmmeter, measure the resistance between the terminals +B and HT. Resistance specification: 11 - 16 ohms at 20°C (68°F).
  4.  
  5. If the resistance is not as specified, replace the sensor.
  6.  
  7. Reconnect the oxygen sensor connector.

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    Fig. Oxygen Sensor testing

  8.  

Single Wire Sensor

Use an analog voltmeter or a digital voltmeter with an analog function to perform this test.

  1. Start the engine and bring it to normal operating temperature, then run the engine above 2500 rpm for 90 seconds or more.
  2.  
  3. Connect the voltmeter between terminals TE1 and E1 of the DLC1 and maintain the engine speed of 2500 rpms.
  4.  
  5. Record the number of times the voltmeter fluctuates in 10 seconds.
  6.  
  7. If the needle fluctuates eight times or more the oxygen sensor is functioning properly.
  8.  
  9. If the needle fluctuates less than eight times in 10 seconds, check that the engine rpm is still 2500 and repeat the test.
  10.  
  11. If the needle still fluctuates less than eight times, disconnect the terminals TE1 and E1 of the DLC1 and maintain the engine speed at 2500 rpm.
  12.  
  13. Measure the voltage between terminals VF1 and E1 . If the voltage is more than zero volts, replace the sensor.
  14.  



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Fig. DLC1 terminal identification for testing the oxygen sensor-1994-95 models

 
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