Neon L4-2.0L SOHC (1995)
the transmission in drive (auto) or in neutral (manual).
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 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 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
-
Fuel contamination
Upstream O2 Sensor Stays at Center
NAME OF CODE:
Upstream O2S Stays at Center
WHEN MONITORED:
With the engine running for more than 2 minutes and engine temperature greater than 170° F.
SET CONDITION:
The upstream oxygen sensor signal voltage is 0.5 volts for 1.5 minutes.
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 open
-
O2 sensor failure
