Neon L4-2.0L SOHC (1995)
and reducing NOx components in the engine exhaust gas. Variations in the signals from this O2 sensor serve as an indicator of oxygen content.
The catalytic converter absorbs the oxygen in the exhaust gas when the fuel/air mixture is lean. The downstream O2 sensor indicates a deficiency
of oxygen when the upstream O2 sensor detects an abundance of oxygen and vice versa.
POSSIBLE CAUSES:
-
Sensor output wire shorted to another circuit
-
Dirty/wet connection causing voltage tracking in connector
-
O2 sensor failure
Downstream O2 Sensor Slow Response
NAME OF CODE:
Downstream O2 Sensor Slow Response
WHEN MONITORED:
With the vehicle engine temperature greater than 170° F and engine speed over 1,600 rpm. Rich response test is conducted when at WOT, with the
front O2 sensor indicating a rich F/A condition. Lean response test is conducted when at closed throttle, in decel fuel shut-off (except SOHC
automatic transmission vehicles), and with the front O2 sensor indicating a lean F/A condition.
SET CONDITION:
The rich response test will fail if the downstream O2 sensor voltage is less than 0.60 volts within 5 seconds of meeting the test conditions. The lean
response test will fail if the downstream voltage is greater than 0.29 volts within 5 seconds of meeting the test conditions. The trouble code will be
set if either (or both) tests fail three times per trip. Once the rich and lean response test each pass once, the testing is complete that trip.
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:
-
Exhaust leak
-
Fuel contamination
-
Electrical wiring connectors
-
Engine mechanical
Downstream O2 Sensor Stays at Center
NAME OF CODE:
Downstream O2 Sensor Stays at Center
WHEN MONITORED:
With the vehicle engine running for over 2 minutes, temperature greater than 170° F, in closed loop.
SET CONDITION:
With oxygen sensor voltage staying between 0.39 volts and 0.52 volts during the trip, the PCM pulls the sensor voltage to 5.0 volts for 30 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
-
Electrical wiring connectors
-
Open ground circuit
-
PCM failure
-
Oxygen sensor failure
O2S Stays Above Center (Rich)
NAME OF CODE:
O2S Stays Above Center (Rich)
