See Figures 1 and 2
The oxygen sensor (O 2 sensor) is a ceramic zirconia bulb which produces an electrical voltage when exposed to the oxygen. The sensor is mounted in the exhaust manifold and is used to detect the amount of oxygen present in the exhaust stream. When there is a large amount of oxygen present (lean mixture), the sensor produces a low voltage. When there is a lesser amount present (rich mixture) it produces a higher voltage. The signal is used by the ECU to pulse the Air/Fuel mixture solenoid, according to the requirements of the engine.
- Start the engine and allow it to reach operating temperature. Turn the engine OFF .
- Connect the positive lead of a multimeter to the O 2 sensor signal wire and the negative lead to the engine ground.
- Start the engine and run at 2000 rpm for two minutes.
- Return the engine to idle and the voltage reading should be fluctuating between 100 and 900 millivolts, as the O 2 sensor detects varying levels of oxygen in the exhaust stream.
Under normal conditions the O2sensor should fluctuate high and low. If the O2sensor voltage does not fluctuate, the sensor may be defective or mixture could be extremely out of range.
Prior to condemning the O
sensor, check the sensor response to changes in the fuel mixture as follows:
- Force the system rich by closing the choke plate. If the O 2 sensor reads now reads above 550 millivolts, the sensor is operating properly and the problems is elsewhere in the system. If the sensor fails to respond, replace the sensor and retest.
- Force the system lean by removing a vacuum line. If this causes the oxygen sensor voltage to read below 350 millivolts the sensor is operating properly and the problems is elsewhere in the system. If the sensor fails to respond, replace the sensor and retest.
Before installing a new oxygen sensor, perform a visual inspection. Black sooty deposits on the O2sensor 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
The oxygen sensor is installed in the exhaust manifold and is removed in the same manner as a spark plug. Always remove electrical connection before trying to remove the sensor. Exercise care when handling the sensor do not drop or handle the sensor roughly; the electrical connector and louvered end must be kept free of grease and dirt. Use an anti-seize compound when installing. Make sure to coat just the threads of the sensor and care should be used not to get compound on the sensor itself. Torque the sensor to 13-17 ft. lbs. (18-27 Nm).