Achieva L4-144 2.4L DOHC VIN T SFI (1996)
Oxygen Sensor: Description and Operation
The Oxygen Sensor (O2S 1)is mounted in the exhaust system where it can monitor the oxygen content of the exhaust gas stream. The oxygen
content in the exhaust reacts with the sensor to produce a voltage output. This voltage ranges from approximately 0.1 volt (high oxygen - lean
mixture) to 0.9 volt (low oxygen - rich mixture). This voltage can be measured with a scan tool.
By monitoring the voltage output of the 02S 1 the PCM will know what fuel mixture command to give to the injectors.
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Lean mixture - low 02S 1 voltage = rich command
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Rich mixture - high 02S 1 voltage = lean command
The 02S 1, if open, should set a DTC P0134. A constant low voltage in the sensor circuit should set a DTC P0131. A constant high voltage in the
circuit should set a DTC P0132. DTC's P0131 and P0132 could also be set as a result of fuel system problems. See DTC tables for conditions that
can cause a lean or rich system.
The Rear Heated Oxygen Sensor (H 02S 2) is used to monitor the oxygen storage capability of the catalytic converter. Similar to the 02S 1, the
HO2S 2 reacts with the oxygen content in the exhaust stream to produce a voltage signal, only after the catalytic converter. This voltage ranges
from approximately 0.1 volt (high oxygen - lean mixture) to 0.9 volt (low oxygen - rich mixture).
Unlike the O2S 1, with a good catalytic converter, the HO2S 2 is normal when its activity appears lazy or inactive. The PCM compares readings
from both the front O2S 1 and the HO2S 2 to determine the catalyst efficiency and will illuminate the MIL if this efficiency falls below a
calibrated level.
