Chrysler RAM50/D50/Arrow 1979-1993 Repair Guide

Oxygen Sensor

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OPERATION



See Figures 1, 2 and 3

With the exception of the 1983-84 models, all Dodge engines use an oxygen sensor to aid in the control of the air/fuel mixture. The ideal mixture within the engine is 14.7 parts of air to one part of fuel. If this ratio can be maintained under all conditions, emissions will be kept to an absolute minimum. The trick is to inform the Engine Control Module (ECM) of any change in conditions so that it can react and make necessary changes. The oxygen sensor is one of many sensors which detect changes during driving.

Located in either the exhaust manifold or the exhaust pipe ahead of the catalytic converter, the oxygen sensor reads the amount of oxygen in the exhaust flow and generates a proportional electrical voltage. This voltage is transmitted to ECM which interprets it and sends necessary messages to fuel and air control components. Remember that the oxygen sensor is reading the result of combustion and reacting to it. If there is a problem in the air/fuel mixture entering the engine, the combustion will be imperfect and the oxygen sensor will generate a signal which shows the error. The signal does not necessarily indicate that the sensor has failed, only that it has detected a different oxygen concentration.



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Fig. Fig. 1: The location of the oxygen (O2) sensor on 2.4L engines-right-hand side of the engine



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Fig. Fig. 2: The location of the O2 sensor harness connector-2.4L engines



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Fig. Fig. 3: The O2 sensor is located in the front exhaust pipe, before the catalytic converter-3.0L engine

Since the oxygen sensor is the furthest "downstream" in the combustion process, it essential to check all other sensors and controls on the engine before assuming this sensor to be bad. Obviously, if the engine is running inefficiently, replacing the oxygen sensor won't cure the problem; the new sensor will continue to correctly read the imperfect exhaust content. About the only failure common to all oxygen sensors is loose or corroded connectors in the electrical wires. If a trouble code indicates an oxygen sensor malfunction, the first place to look is at the connector, making sure the pins are clean and fit tightly together. The low voltages flowing in this system can be changed or blocked by a high resistance (poor) connection.

HARNESS TESTING



2.4L Engines

See Figure 4

The 1993, rear-wheel drive 2.4L (California) Pick-ups have the same engine controls as the 3.0L engines. All other 2.4L engines are listed as 2.4L engines.

  1. Unplug both the harness connector going to the oxygen sensor and the ECM harness connector. Check for an open-circuit or a short-circuit to ground, between ECM terminal 4 and the oxygen sensor terminal 1. If there is a short or open-circuit found, repair the harness between the two terminals.
  2.  
  3. Check for continuity of the ground circuit (oxygen sensor connector terminal 2). If there is continuity, the harness is good, otherwise repair the harness between oxygen sensor terminal 2 and the ground.
  4.  



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Fig. Fig. 4: The O2 sensor harness connector terminals - 2.4L engines

3.0L Engine See Figure 5

  1. Unplug the MFI relay connector and the oxygen sensor connector. By touching the ohmmeter probes to both ends of the harness, check for continuity between the O 2 sensor and the MFI relay terminals. If no continuity is found, repair or replace the harness between the two terminals 5 and O 2 sensor terminal 1.
  2.  
  3. Unplug the ECM harness connector and plug the MFI relay connector back in. Check for an open-circuit or a short-circuit to ground between the O 2 sensor and the ECM. If there is a short or open-circuit, repair or replace the harness between the two terminals. ECM terminal 4 and O 2 sensor terminal 4.
  4.  
  5. Check for continuity in the ground circuit. If no continuity is found, repair or replace the harness between the terminals. ECM terminal 17 and 24 and O 2 sensor terminal 2, Ground circuit and O 2 sensor terminal 3.
  6.  



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Fig. Fig. 5: The O2 sensor harness connector terminals-3.0L engine

COMPONENT TESTING



2.OL, 2.4L. and 2.6L Engines

The 1993, rear-wheel drive 2.4L (California) Pick-ups have the same engine controls as the 3.0L engines. All other 2.4L engines are listed as 2.4L engines.

  1. Before testing, warm the engine to normal operating temperature. Coolant temperature must be 80-85-°C (175-185-°F) or more.
  2.  

An accurate digital voltmeter is required for this test.

  1. Shut the engine OFF . Disconnect the oxygen sensor connector and connect the positive probe of the voltmeter to the sensor connector.
  2.  
  3. Ground the negative probe of the meter to the body or the engine as convenient but do not ground it back to the sensor or connect it to the second terminal.
  4.  
  5. Place the meter where it can be seen from the driver's seat. Start the engine.
  6.  
  7. Race the engine to about 4000 rpm and observe the meter; it should show about 1 volt (600-1000 mV).
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  9. Shut the engine OFF , remove the test equipment and reconnect the sensor harness.
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  11. If the sensor does not show this value, replace it with a new one.
  12.  

3.0L Engine

  1. Unplug the connector to the O 2 sensor, then use the test harness (MD998464) to link the connector and the sensor together.
  2.  
  3. Check that there is continuity between terminal 1 (black clip of the test harness) and terminal 3 (white clip) of the O 2 sensor connector. There should be approximately 20 ohms at 68-°F (20-°C).
  4.  
  5. If there is no continuity, replace the O 2 sensor.
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  7. Warm the engine until the coolant temperature is 176-°F (80-°C) or higher.
  8.  
  9. Using jumper wires, connect terminal 1 (black clip) and terminal 3 (white clip) of the O 2 sensor with the positive battery terminal and negative battery terminal respectivly.
  10.  


WARNING
When connecting the jumper wires, be careful not to connect them to the wrong terminals, since this could damage the O2sensor. The terminals should be terminal 1 (+) and terminal 3 (-).

  1. Connect a digital voltmeter to terminal 2 (red clip) and terminal 4 (blue clip).
  2.  
  3. While repeatedly racing the engine, measure the O 2 sensor's output voltage. The voltage should measure between 0.06-1.0 volts.
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  5. If the measurements are not as specified, the cause is probably a malfunction of the O 2 sensor.
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REMOVAL & INSTALLATION



See Figure 6


CAUTION
Perform this work only after the exhaust system has cooled enough to avoid burns.

It is more common to remove the oxygen sensor for protection or access during other repairs than to replace it because of failure. Once the sensor is removed, it must be protected from impact and/or chemical contact. Never attempt to clean the tip with solvent and never allow the tip to contact grease, oil or other chemicals. The zirconia element in the tip will be polluted and the sensor will function poorly, if at all.

  1. Locate the oxygen sensor. On 4-cylinder engines, it will be located in the exhaust manifold, usually mounted either underneath or from the side. The 6-cylinder engines have the oxygen sensor mounted in the exhaust pipe, just beyond the Y where the left and right pipes connect into one.
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  3. Follow the wiring from the sensor to the first connector and disconnect it. Do not attempt to disconnect the wiring at the sensor.
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  5. Particularly on non-turbocharged, 4-cylinder engines, the sensor may be obstructed by heat shields on the exhaust manifold. Remove them as necessary.
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  7. Install the proper size wrench on the flats of the sensor. Place the socket on the sensor and use a box wrench to turn the socket.
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  9. Keeping the wrench (or socket) square to the sensor while removing it. Do not allow the wrench to become crooked or to come off the flats. Remember that the sensor has been exposed to extreme temperature and corrosive exhaust gasses. It may be difficult to remove.
  10.  
  11. Once the sensor is removed, place it in a clean, protected location.
  12.  



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Fig. Fig. 6: The O2 sensor is accessible from the underside of the exhaust manifold--2.6L engine shown

To install:
  1. The threads of the sensor may be lightly coated with an anti-seize compound but extreme care must be taken to protect the tip and shield area of the sensor from even the slightest contamination.
  2.  
  3. Handle the oxygen sensor carefully, protecting it from impact, and install it in place. Start the threads by hand and hand-tighten it as far as possible.
  4.  
  5. Finish by tightening the sensor to 33 ft. lbs. (45 Nm).
  6.  
  7. Install the heat shields if any were removed. Tighten the bolts to 12 ft. lbs. (16 Nm).
  8.  
  9. Connect the sensor wiring to the harness connector. Make certain the wiring is correctly run and out of the way of hot or moving components.
  10.  

 
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