Chrysler Full-Size Trucks 1989-1996 Repair Guide

Oxygen Sensor

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OPERATION



See Figures 1 and 2

The oxygen sensor is located in the exhaust manifold and is a device which produces an electrical voltage when exposed to the oxygen present in the exhaust gases. The sensor is electrically heated for more efficient monitoring when the engine is running. When a large amount of oxygen is present (lean mixture), the oxygen sensor produces a low voltage. When there is less oxygen present (rich mixture), the sensor produces a high voltage.



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Fig. Fig. 1: A single oxygen sensor-4-cylinder, V6 and light duty 5.2L and 5.9L V8 engines



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Fig. Fig. 2: A dual oxygen sensor arrangement-heavy duty V8 and V10 engines

By monitoring the oxygen content and converting it into a voltage signal, the sensor acts as a rich/lean switch for the SMEC/SBEC computer, which regulates the fuel delivery to compensate accordingly.

The oxygen sensor is located in the exhaust manifold or the Y-pipe on the right side of the vehicle. A special tool (C-4907) is necessary for sensor removal and installation.

TESTING



  1. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
  2.  
  3. Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (02S) and battery ground.
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  5. Verify that the 02S voltage fluctuates rapidly between 0.40-0.60 volts.
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  7. 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.
  8.  
  9. If the 02S voltage stabilizes at either end of the specified range, the engine controller is probably not able to compensate for a mechanical problem such as a vacuum leak or a high float level. 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.
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  11. 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.
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  13. 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.
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  15. 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.
  16.  

REMOVAL & INSTALLATION



See Figure 3

On 2.5L engines, the oxygen sensor is located on the exhaust manifold. On 3.9L engines, the oxygen sensor is located in the exhaust Y-pipe. On 5.2L and light duty 5.9L engines, it is located above the outlet of the left exhaust manifold. On heavy duty 5.9L and 8.0L engines, dual oxygen sensors are found on each exhaust downpipe.



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Fig. Fig. 3: Remove the oxygen sensor with a flange wrench or appropriate socket-V6 engine shown


CAUTION
The exhaust manifold/pipe get extremely hot during engine operation and if touched can cause severe burns. If servicing the oxygen sensor when the engine is hot, avoid contact with the exhaust manifold or pipe.

A special tool C-4907, or a box wrench or a suitable oxygen sensor wrench is required to remove the oxygen sensor. Do not pull on the oxygen sensor wires!

  1. Disconnect the wiring harness from the oxygen sensor.
  2.  
  3. Remove the sensor using the appropriate tool.
  4.  

The oxygen sensor threads are coated with an anti-seize compound. The compound must be removed from the mounting boss threads, either in the exhaust manifold or Y-pipe. An 18mm x 1.5 x 6E tap is required.

To install:
  1. Clean the threads of the mount to remove any old anti-seize compound.
  2.  
  3. If the old sensor is to be reused, apply anti-seize compound to its threads. Be very careful not to get any compound on the sensor flutes which protrude into the manifold. If you contaminate the sensor, you'll ruin it. New sensors come with the compound already applied.
  4.  
  5. Install and tighten the sensor to 20 ft. lbs. (27 N.m). Connect the wiring harness.
  6.  

 
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