Chrysler Neon 1995-1999 Repair Guide

Heated Oxygen Sensor

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OPERATION



See Figures 1 and 2

As a vehicle accrues mileage, the catalytic converter deteriorates. The deterioration results in a less effective catalyst. To monitor catalytic converter deterioration, the fuel injection system uses two heated oxygen sensors. One sensor upstream of the catalytic converter and one downstream of the converter.



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Fig. Fig. 1: The upstream heated oxygen sensor is threaded into the outlet flange of the exhaust manifold

The PCM compares the reading from the sensors to calculate the catalytic converter oxygen storage capacity and storage efficiency. Also the PCM uses the upstream heater oxygen sensor input when adjusting the injector pulse width. When the catalytic converter efficiency drops below preset emission criterion, the PCM stores a Diagnostic Trouble Code (DTC) and illuminates the Malfunction Indicator Lamp (MIL).



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Fig. Fig. 2: The downstream heated oxygen sensor is threaded into the exhaust pipe behind the catalytic converter

The automatic shutdown relay supplies battery voltage to both of the heated oxygen sensors. The sensors have heating elements which reduce the amount of time it takes for the sensors to reach operating temperature.

TESTING



See Figure 3

  1. Visually check the connector, making sure it is properly attached and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. Use an ohmmeter to test the heating element of the heated oxygen sensors.
  4.  
  5. Detach the electrical connector from each oxygen sensor. The white wires in the sensor connector are the power and ground circuits for the heater elements.
  6.  
  7. Connect the ohmmeter test leads to the terminals of the white wires in the heated oxygen sensor connector.
  8.  



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Fig. Fig. 3: Test resistance with an ohmmeter. This 1995 vehicle is within specifications

  1. Replace the heated oxygen sensor is the resistance is not 5-7 ohms for 1995 vehicles or 4-7 ohms for 1996-99 vehicles.
  2.  

  1. Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (02S) signal wire and battery ground.
  2.  
  3. Verify that the 02S voltage fluctuates rapidly between 0.40-0.60 volts.
  4.  
  5. If the 02S voltage is stabilized at the middle of the specified range (approximately 0.45-0.55 volts) or if the 02S voltage fluctuates very slowly between the specified range (02S signal crosses 0.5 volts less than 5 times in ten seconds), the 02S may be faulty.
  6.  
  7. If the 02S voltage stabilizes at either end of the specified range, the PCM is probably not able to compensate for a mechanical problem such as a vacuum leak or a faulty pressure regulator. These types of mechanical problems will cause the 02S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the 02S test repeated.
  8.  
  9. Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a lean mixture condition. Reattach the vacuum hose.
  10.  
  11. Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a rich mixture condition.
  12.  
  13. If the 02S voltage is above or below the specified range, the 02S and/or the O2S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.
  14.  

Before installing a new oxygen sensor, perform a visual inspection. Black, sooty deposits on the sensor 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 contaminants can damage a new sensor.

REMOVAL & INSTALLATION



Upstream Heated Oxygen Sensor

See Figures 4 and 5

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



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Fig. Fig. 4: Upstream heated oxygen sensor (1) and wiring (2)

  1. Unplug the upstream oxygen sensor connector.
  2.  
  3. Remove the sensor using a suitable oxygen sensor crow foot wrench. After removing the sensor, the exhaust manifold must be cleaned with an 18mm x 1.5 + 6E tap.
  4.  



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Fig. Fig. 5: Use a crow foot wrench to loosen the upstream heated oxygen sensor

To install:
  1. New oxygen sensors will be packaged with a special anti-seize compound already applied to the threads. If you a reinstalling the old sensor, the sensor threads must be coated with fresh anti-seize compound. You must use the correct type of anti-seize compound containing liquid graphite and glass beads. This is not a conventional anti-seize paste. the graphite will tend to burn away, but the glass beads will remain. The use of a regular compound may electrically insulator the sensor, rendering it inoperative. You must coat the threads with an electrically conductive anti-seize compound.
  2.  
  3. Carefully thread the sensor into the bore, then tighten to 20 ft. lbs. (28 Nm).
  4.  
  5. Attach the oxygen sensor electrical connector.
  6.  
  7. Carefully lower the vehicle, then connect the negative battery cable.
  8.  

Downstream Heated Oxygen Sensor

See Figures 6, 7, 8, 9 and 10

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



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Fig. Fig. 6: The downstream O2 sensor is threaded into the exhaust pipe behind the catalytic converter

  1. Unplug the electrical connector from the downstream oxygen sensor.
  2.  



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Fig. Fig. 7: Location of the downstream oxygen sensor connector (see arrow)

  1. Detach the sensor electrical harness from the clips along the body.
  2.  
  3. Remove the sensor using a suitable oxygen sensor crow foot wrench. After removing the sensor, the exhaust manifold must be cleaned with an 18mm x 1.5 + 6E tap.
  4.  



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Fig. Fig. 8: Because the angle, you should use a crow foot wrench to remove the downstream oxygen sensor



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Fig. Fig. 9: There are also special sockets available specifically for the purpose of removing the sensor



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Fig. Fig. 10: Remove the oxygen sensor from the exhaust pipe

To install:
  1. New oxygen sensors will be packaged with a special anti-seize compound already applied to the threads. If you a reinstalling the old sensor, the sensor threads must be coated with fresh anti-seize compound. You must use the correct type of anti-seize compound containing liquid graphite and glass beads. This is not a conventional anti-seize paste. the graphite will tend to burn away, but the glass beads will remain. The use of a regular compound may electrically insulator the sensor, rendering it inoperative. You must coat the threads with an electrically conductive anti-seize compound.
  2.  
  3. Carefully thread the sensor into the bore, then tighten to 20 ft. lbs. (28 Nm).
  4.  
  5. Route the sensor electrical harness through the clips along the body.
  6.  
  7. Attach the oxygen sensor electrical connector.
  8.  
  9. Carefully lower the vehicle, then connect the negative battery cable.
  10.  

 
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