Neon L4-2.0L DOHC (1996)
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Dirt/moisture/grease inside connector
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Fuel contamination
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Engine mechanical
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Weak upstream O2 sensor with deteriorated catalyst
Upstream O2 Sensor Heater Failure
Name of Code:
Upstream O2 Sensor Heater Failure
When Monitored:
With the Ignition key off, after the engine cools down.
Set Condition:
No sensor output signal is received when the PCM powers up the sensor heater.
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 signal is controlling the air/fuel ratio. Variations in the signals from the 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. The heater element helps the 02 sensor quickly reach a normal and steady operating temperature. which is required for
proper emission control.
Possible Causes:
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Open heater element circuit
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02 sensor failure
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PCM failure
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Dirt/moisture/grease inside connector
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02 sensor heater wires
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ASD relay failure
Upstream O2 Sensor Shorted to Voltage
Name of Code:
Upstream 02 Sensor Shorted to Voltage
When Monitored:
With the ignition key on.
Set Condition:
The engine running for more than 2 minutes and coolant temperature above 176°F. The upstream oxygen sensor signal voltage is above 1.2 volts
for 2.6 seconds.
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:
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Sensor output wire shorted to another circuit
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Dirty/wet connection causing voltage tracking in connector
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02 sensor failure
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Powertrain control module failure
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Connector terminals
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Connector wires
Upstream O2 Sensor Slow Response
Name of Code:
Upstream O2 Sensor Slow Response
When Monitored: