See Figure 1
The oxygen sensor has the ability to produce a low voltage signal that feeds information on engine exhaust oxygen content to the control module.
The sensor is constructed from a zirconia/platinum electrolytic element. Zirconia is an electrolyte that conducts electricity under certain chemical conditions. The element is made up of a ceramic material which acts as an insulator when cold. At operating temperatures of approximately 600°F (315°C), the element becomes a semiconductor. A platinum coating on the outer surface of the element stimulates further combustion of the exhaust gases right at the surface and this helps to keep the element up to the desired temperature.
The oxygen sensor has an inner cavity which is filled with reference (atmospheric) air. The atmosphere has approximately 21 percent oxygen in it. In the circuit, this inner cavity is the positive terminal, while the outer surface (exposed to the exhaust stream) is the negative or ground terminal.
Due to the element's electrolytic properties, oxygen concentration differences between the reference air and exhaust gases produce small voltages. A rich exhaust (excess fuel) has almost no oxygen. So when there is a large difference in the amount of oxygen touching the inside and outside surfaces, more conduction occurs and the sensor puts out a voltage signal above 0.6 V (600 mV). The signal may vary as high as 0.9 V (999 mV).
With a lean exhaust (excessive oxygen), there is about 2 percent oxygen in the gases. The smaller difference in oxygen content causes less conduction and the sensor produces a smaller voltage somewhere below 0.3 V (300 mV). The signal could drop as low as 0.1 V (100 mV). Commonly, values outside this range will cause a trouble code to set for most control systems. When handling the oxygen sensor, follow these precautions:
This test requires the use of a scan tool.
- Run the engine at normal operating temperature and connect a scan tool.
- Disconnect the oxygen sensor. Jumper the purple wire to ground.
- The scan tool should display O 2 voltage below 0.2 volts (200 MV). If it does, then O 2 sensor or sensor connection is faulty and must be replaced. If not, proceed to the following step.
With the ignition
and the engine off, check the voltage of the tan wire leading to the ECM/PCM using a Digital Voltmeter (DVM). The voltage should be 0.3-0.6 volts (300-600 MV).
- If the voltage reading is 0.3-0.6 volts, the ECM/PCM is faulty.
- If the voltage reading is over 0.6 volts, the wire is open, the connection is faulty or the computer control module is faulty.
- If the voltage reading is under 0.3 volts, the computer control module connections or computer control module is faulty.
REMOVAL and INSTALLATION
See Figures 2 and 3
- Disconnect the negative battery cable.
- Detach the sensor electrical connector.
- Carefully remove the Oxygen (O 2 ) sensor.
A special anti-seize compound is used on the O2sensor threads. This compound is made up of a liquid graphite and glass beads. The graphite will burn away, but the glass beads will remain, making the sensor easier to remove. New or service sensors will already have the compound applied to the threads. If a sensor is removed from the engine, and is to be reinstalled, the threads must have anti-seize compound applied prior to reinstallation.
- If reinstalling the old sensor, coat the threads of the sensor with anti-seize compound 5613695 or equivalent.
- Install the sensor and tighten it to 30 ft. lbs. (41 Nm).
- Attach the sensor electrical connector.
- Connect the negative battery cable.