Chrysler Front Wheel Drive Cars 6-CYL 1988-1995 Repair Information

Oxygen Sensor

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DESCRIPTION



See Figures 1 and 2

The oxygen sensor is a device which produces an electrical voltage when exposed to the oxygen present in the exhaust gases. The oxygen sensor is electrically heated internally for faster switching when the engine is running. When there is a large amount of oxygen present (lean mixture), the sensor produces a low voltage. When there is a lesser amount present (rich mixture) it produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch. The voltage is transmitted to the control module which adjusts the fuel injection pulse. The sensor is mounted in the turbo outlet or rear exhaust manifold.



Click image to see an enlarged view

Fig. Fig. 1: Heated oxygen sensor location-except Premier and Monaco



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Fig. Fig. 2: Oxygen sensor location on all Premier and Monaco vehicles

If the engine exhibits high hydrocarbon and carbon monoxide emissions, this may indicate that the oxygen sensor is at fault. The sensor may also fail in a lean mode, which would produce low emissions but slightly lean running, so that engine operation would be just slightly rough. The sensor should be replaced at the correct maintenance interval for that year and model (refer to the maintenance intervals chart) as a matter of routine maintenance. An anti-seize compound such as Loctite 771-64® is recommended to ease subsequent removal of the sensor.

TESTING



Except Premier and Monaco
1988-90 MODELS
  1. Start the engine and allow it to reach operating temperature. Turn the engine OFF .
  2.  
  3. Connect the positive lead of a multimeter to the O 2 sensor signal wire and the negative lead to the engine ground.
  4.  
  5. Start the engine and run at 2000 rpm for two minutes.
  6.  
  7. Return the engine to idle. The voltage reading should fluctuate between 100-900 millivolts, as the O 2 sensor detects varying levels of oxygen in the exhaust stream.
  8.  

Under normal conditions, the O2sensor should fluctuate high and low. If the O2sensor voltage does not fluctuate, the sensor may be defective or the mixture could be out of range (too rich or lean).

  1. Before replacing the O 2 sensor, check the sensor response to changes in the fuel mixture as follows: lean out the system by removing a vacuum line. If this causes the oxygen sensor voltage to read below 350 millivolts the sensor is operating properly; the problem is elsewhere in the system. If the sensor fails to respond, replace the sensor with a new one, then retest.
  2.  

Before installing a new oxygen sensor, perform a visual inspection. Black sooty deposits on the O2sensor tip may indicate a rich air/fuel mixture. White gritty deposits could be an internal antifreeze leak. Brown deposits indicate oil consumption. All of these containments can damage a new sensor.

1991-95 MODELS
  1. Run the engine until normal operating temperature is reached, then allow the engine to idle.
  2.  
  3. Inspect the engine for any abnormal vacuum conditions. Correct any vacuum leaks found.
  4.  
  5. Using a voltmeter, measure the voltage by backprobing the oxygen sensor connector from the black/dark green wire to an engine ground.
    1. If the oxygen sensor voltage fluctuates (as it detects varying levels of oxygen in the exhaust gas), and no trouble code has been registered for the oxygen sensor, the oxygen sensor is functioning correctly. Stop the test.
    2.  
    3. If the voltage is steady and above 0.10 volts, continue to Step 5.
    4.  
    5. If the voltage is steady and below 0.10 volts, refer to Step 4.
    6.  

  6.  

Under normal conditions, the O2sensor should fluctuate high and low. If the O2sensor voltage does not fluctuate, the sensor may be defective or the mixture could be out of range (too rich or lean).

  1. If the voltage was below 0.10 volts, perform the following:
    1. Turn the ignition OFF .
    2.  
    3. Unplug the oxygen sensor connector.
    4.  
    5. Measure the oxygen sensor wiring circuit to the PCM, and if the resistance of the circuit above 10.0 ohms, replace the oxygen sensor with a new one. Otherwise, repair the circuit itself.
    6.  

  2.  
  3. Replace the oxygen sensor with a new one, then retest the sensor system.
  4.  

Premier and Monaco

The oxygen sensor heating element can be tested by connecting an ohmmeter test leads to terminals A and B of the sensor connector. Resistance should be below 10 ohms. Replace the sensor if an infinite reading is obtained.

REMOVAL & INSTALLATION

Except Premier and Monaco

See Figures 1 and 3

To remove the oxygen sensor, a special removal tool is needed. Use the special tool C-4907 or the equivalent to unthread the sensor from the exhaust system. It is necessary to be able to adapt this tool to a torque wrench. A tap is also required to clean the sensor mounting threads.

The heated oxygen sensor is located in the exhaust manifold on all vehicles except Premier and Monaco.

  1. Make sure the engine has been off for several hours so that all parts have cooled sufficiently for safe handling.
  2.  
  3. Pull on the plug (not the wiring) to disconnect the oxygen sensor electrical lead.
  4.  



Click image to see an enlarged view

Fig. Fig. 3: This special tool will be needed to extract the sensor from the exhaust manifold-except Premier and Monaco vehicles

  1. Install the special tool and unscrew the sensor from the exhaust manifold.
  2.  
  3. Turn the tap into the sensor threads to clear any corrosion or dirt.
  4.  

To install:

If installing a new sensor, make sure to get the proper replacement parts.

  1. Coat the threads with Loctite 771-64® (or equivalent) anti-seize compound. Insert and tighten the sensor to 20 ft. lbs. (27 Nm).
  2.  
  3. Plug the electrical connector back into the sensor.
  4.  

Premier and Monaco

See Figure 2

The heated oxygen sensor is located in the front Y-pipe on Monaco and Premier vehicles.

  1. Make sure the engine has been off for several hours so that all parts have cooled sufficiently for safe handling.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Raise and safely support the front of the vehicle on jackstands.
  6.  
  7. Pull on the plug (not the wiring) to disconnect the oxygen sensor electrical lead.
  8.  
  9. Unscrew the sensor from the Y-pipe.
  10.  
  11. Turn the tap into the sensor threads to clear any corrosion or dirt.
  12.  

To install:

If installing a new sensor, make sure to get the proper replacement parts.

  1. Coat the sensor's threads with Loctite 771-64® (or equivalent) anti-seize compound. Insert and tighten the sensor to 20 ft. lbs. (27 Nm).
  2.  
  3. Plug the electrical connector back into the sensor.
  4.  
  5. Lower the vehicle.
  6.  
  7. Connect the battery cable.
  8.  

 
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