Ram Truck 1500, 2500 & 3500 (2006-2008)

Heated Oxygen Sensor

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Operation



3.7L, 4.7L & 5.7L Engines

The HO2S detects the presence of oxygen in the exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a voltage signal greater than 0.6 volt. The HO2S provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1during closed loop engine operation. The HO2S generates a voltage between 0.0 and 1.1 volts.

Embedded with the sensing element is the HO2S heater. The heating element heats the sensor to a temperature of 800°C (1,472°F). At approximately 300°C (572°F) the engine can enter closed loop operation. The PCM turns the heater on by providing the ground when the correct conditions occur. The heater allows the engine to enter closed loop operation sooner.

6.7L Diesel Engine

The engine aftertreatment system monitors the O2 content in the diesel engine exhaust. The ECM monitors the exhaust gases for oxygen content and varies the rich/lean fuel mixture of the intake air fuel mixture to adjust the system. This diagnostic monitors the status message broadcast by the Smart O2 sensor module for the upstream O2 sensor circuit. The ECM will set the fault if it receives a FMI (Failure Mode Indicator) message from the Smart O2 Module. The ECM will illuminate the MIL lamp immediately when the diagnostic runs and fails. The ECM will turn off the MIL lamp diagnostic runs and passes in four consecutive drive cycles

Removal & Installation



3.7L, 4.7L & 5.7L Engines

CAUTION
The exhaust manifold, exhaust pipes and catalytic converter become very hot during the engine operation. Allow engine to cool before removing oxygen sensor.

  1. Before servicing the vehicle, refer to the Precautions section.
  2.  
  3. Raise and support vehicle.
  4.  
  5. Disconnect wire connector from O2S sensor.
    WARNING
    When disconnecting sensor electrical connector, do not pull directly on wire going into sensor.

  6.  
  7. Remove the HO2S sensor with an oxygen sensor removal and installation tool.
  8.  
  9. Clean threads in exhaust pipe using appropriate tap.
  10.  

To install:


NOTE
Threads of new oxygen sensors are factory coated with anti-seize compound to aid in removal. DO NOT add any additional anti-seize compound to threads of a new oxygen sensor.

  1. Install the HO2S sensor. Tighten to 30 ft. lbs. (41Nm).
  2.  
  3. Connect the HO2S sensor wire connector.
  4.  
  5. Lower the vehicle.
  6.  

6.7L Diesel Engine
  1. Raise and support vehicle
  2.  
  3. Disconnect wire connector from O2S sensor.
    WARNING
    When disconnecting sensor electrical connector, do not pull directly on wire going into sensor.

  4.  
  5. Remove the HO2S sensor with an oxygen sensor removal and installation tool.
  6.  
  7. Clean threads in exhaust pipe using appropriate tap.
  8.  

To install:


NOTE
Threads of new oxygen sensors are factory coated with anti-seize compound to aid in removal. DO NOT add any additional anti-seize compound to threads of a new oxygen sensor.

  1. Install the HO2S sensor. Tighten to 30 ft. lbs. (41Nm).
  2.  
  3. Connect the HO2S sensor wire connector.
  4.  
  5. Lower the vehicle.
  6.  

Testing



3.7L, 4.7L & 5.7L Engines

This procedure checks the heater circuit of the HO2S.

  1. Warm up the engine until operating temperature is reached.
  2.  
  3. Turn the ignition off.
  4.  
  5. Wait a minimum of 8 minutes to allow the O2 Sensor to cool down before continuing the test. Allow the O2 Sensor voltage to stabilize between 4.6-5.0 volts.
  6.  
  7. With the ignition on, engine not running.
  8.  
  9. Install a scan tool, actuate the HO2S heater test.
  10.  
  11. With the scan tool, monitor O2 Sensor voltage for at least 2 minutes.
  12.  
  13. If the voltage stays above 4.5 volts, turn the ignition off. (If not problem maybe intermittent).
  14.  
  15. Allow the O2 sensor to cool down to room temperature.
  16.  
  17. Disconnect the HO2S sensor harness connector.
  18.  
  19. Measure the resistance of the O2 heater element, between the HO2S heater control terminal and the O2 heater ground terminal in the HO2S sensor connector.
  20.  
  21. HO2S heater element resistance values should be measured at 21.1°C (70°F). The resistance value will vary with different temperature values.
  22.  
  23. The resistance of the HO2S sensor heater element should be between 2.0-30.0 ohms.
  24.  
  25. If the resistance is not as stated replace the HO2S sensor.

    Click image to see an enlarged view

    Fig. Typical HO2S sensor harness connector

  26.  

6.7L Diesel Engine
  1. Disconnect the HO2S sensor harness connector.
  2.  
  3. Measure the resistance of the 02 sensor heater between the K99 (Pin 4) 02 heater supply and K79 (Pin 3) 02 heater return circuits. Readings are taken on the component side.
  4.  
  5. The resistance should be approximately 3.2 +/- 0.8 ohms at ambient temperature.
  6.  
  7. If the reading was not as stated, replace the HO2S Sensor.

    Click image to see an enlarged view

    Fig. HO2S 6.7L diesel engine sensor side of component

  8.  

 
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