Neon L4-2.0L DOHC (1996)
Theory of Operation:
The upstream oxygen sensor is a voltage generating device. The PCM receives exhaust gas information from this O2 sensor. The sensor detects
exhaust gas content by a galvanic reaction within the sensor that produces a voltage. After measuring the amount of oxygen in the exhaust gases,
the upstream oxygen sensor tells the PCM how well its output signals are controlling the air/fuel ratio. Variations in the signal from this O2 sensor
serve as air/fuel ratio indicators. Changes in the sensor signal occur because the air/fuel ratio is constantly changing. When oxygen content is low
(rich mixture), the voltage signal will be approximately 1 volt. When oxygen content is high (lean mixture), the voltage signal will be low,
approximately 0.1 volt.
Possible Causes:
-
Sensor output wire shorted to another circuit
-
Dirty/wet connection causing voltage tracking in connector
-
O2 sensor failure
-
Powertrain control module failure
-
Connector terminals
-
Connector wires
Downstream O2 Sensor Stays at Center
Name of Code:
Downstream O2 Sensor Stays At Center
When Monitored:
With the vehicle engine running for more than two minutes, engine temperature greater than 170°F, in closed loop.
Set Condition:
If oxygen sensor voltage stays between 0.29 volts and 0.72 volts for 30 seconds, the PCM pulls the sensor voltage to 5.0 volts for 60 seconds and
monitors the sensor voltage. If the voltage stays at 5.0 volts, this trouble code will set, indicating no activities.
Theory of Operation:
Effective control of exhaust emissions is achieved by an oxygen feedback system. The downstream oxygen sensor (O2S), located in the exhaust
path, monitors the exhaust emissions. Once the sensor reaches its normal operating temperature of 300°-350° C (572°-662° F), it generates a
voltage inversely proportional to the amount of oxygen in the exhaust. This voltage is used to calculate the efficiency of the catalytic converter.
The downstream oxygen sensor is monitored for proper response to assure a correct catalytic converter efficiency calculation. A good sensor will
indicate a rich condition when at WOT (due to the enriched F/A ratio), and a lean condition when in decel fuel shut-off (due to the lean F/A ratio).
Possible Causes:
-
Sensor output wire open
-
Dirt/moisture/grease inside connector
-
Open ground circuit
-
Oxygen sensor failure
-
PCM failure
Slow Upstream O2 Sensor During Catalyst Monitor
Name of Code:
Slow Upstream O2 Sensor During Catalyst Monitor
When Monitored:
With the engine running, coolant greater than 17O°F, open throttle, steady to slightly increasing vehicle speed between 18 MPH and 55 MPH,
with a light load on the engine, for a period no less than five minutes.
Set Condition:
The upstream oxygen sensor signal voltage is switching from below 0.39 volt to above 0.6 volt and back fewer times than required.
Theory of Operation:
Effective control of exhaust emissions is achieved by an oxygen feedback system, of which the most important element is the upstream oxygen
sensor (O2S). which is located in the exhaust path. Once the sensor reaches its normal operating temperature of 30O° to 350°C (572° to 662°F), it
generates a voltage inversely proportional to the amount of oxygen in the exhaust. This voltage is used to calculate the fuel injector pulse width,
which maintains the optimum 14.7 to 1 air/fuel (A/F) ratio that is required for the catalytic converter to best control exhaust emissions. Response
rate is the time required for the sensor to detect changes in the exhaust gas oxygen content; it switches from lean to rich if it is exposed to a richer
than optimum A/F mixture, or vice versa. The O2S output voltage ranges from 0 to 1 volt. A good sensor easily generates an output voltage in this
range as it is exposed to different oxygen concentrations. To detect a shift in the A/F mixture (lean or rich), the output voltage has to change
beyond a threshold value. A malfunctioning sensor could have difficulty changing beyond the thresholds.
Possible Causes:
-
Exhaust leak
