BMW Coupes and Sedans 1970-1988 Repair Guide

Oxygen Sensor System

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See Figures 1 and 2

An oxygen (lambda) sensor system is used on all models equipped with a 3-way catalyst. No exhaust gas recirculation is required. Completely burned fuel in the form of carbon monoxide is used, within the catalyst, to remove oxygen from the nitrogen oxide emissions, leaving them in their normal state as nitrogen. This process can only be accomplished if the fuel/air ratio is kept precisely at the optimum level with no excess air or oxygen. A sensor located in the exhaust gas stream constantly regulates the fuel/air mixture provided by the injection system according to the amount of air (oxygen) in the exhaust.



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Fig. Fig. 1: Oxygen sensor system-320i model with catalytic converter



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Fig. Fig. 2: Example of an oxygen sensor

MAINTENANCE



Every 30,000 miles (48,000 km) an oxygen sensor warning light will indicate the need to change the oxygen sensor. The warning light must be reset when the sensor is replaced by pushing the reset button on the mileage switch under the hood.

REMOVAL & INSTALLATION



See Figures 3, 4, 5, 6 and 7

  1. Disconnect the electrical sensor lead.
  2.  

On some models the connection is beneath the vehicle, next to the exhaust system. On other models, the connection is in the engine compartment.


CAUTION
Severe burns can result from a hot exhaust system. Be sure that the exhaust system is cold before proceeding.

  1. Unscrew the oxygen sensor from the exhaust manifold.
  2.  

To install:
  1. Coat the replacement sensor threads with anti-seize compound.
  2.  

Do not get any anti-seize compound on the sensor body, as it will ruin the sensor.

  1. Thread the new sensor into the exhaust manifold and tighten to 3.5 ft. lbs. (5 Nm).
  2.  



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Fig. Fig. 3: Unfasten the oxygen sensor wire connection



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Fig. Fig. 4: An oxygen sensor mounted in the exhaust pipe. Some models are equipped with a protective shield around the sensor



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Fig. Fig. 5: Unclip the shield, if so equipped



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Fig. Fig. 6: Unscrew the oxygen sensor



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Fig. Fig. 7: Before installing the oxygen sensor, apply anti-seize compound to the threads. Do not get any on the probe end of the sensor

  1. Reset the service interval switch and make sure the dash warning light is out.
  2.  
  3. Retest the CO level using an exhaust analyzer with the oxygen sensor disconnected. If the CO level fails to drop when the sensor is reconnected, there is a fault in the system.
  4.  

 
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