There are several different models of Saturns. This info is for an SC1.
The heated oxygen sensor (H02S-2) is mounted behind the catalytic converter. This sensor is used to determine the oxygen storage capability of the catalytic converter. Oxygen storage capability is used as a measure of converter condition, and its ability to perform its function. Due to the location of the rear HO2S, it requires additional heat to operate properly. This sensor incorporates a heater (12 ohms), powered by ignition voltage which allows the sensor to remain functional under most operating conditions. In order to determine that the sensor heater is functioning, its function can only be tested after what is considered a cold start. The PCM will monitor airflow and the time it takes for the sensor to become functional. If a start up is considered to be a hot restart the heater function cannot be tested due to the amount of heat stored by the catalytic converter. Also if airflow after start up is too high the sensor will not be tested due to the amount of heat generated by the engine making it difficult to accurately diagnose a heater malfunction.
DTC P0141 will set if the H02S-2 voltage does not change by more than 150 mv after 100 to 190 seconds (exact time depends on start-up coolant temp and airflow after start-up) when:
" Engine coolant temperature (ECT) and intake air temperature are within 10 C (50 F) of each other.
" Average airflow less than 17 grams/sec.
" The test is run once per ignition cycle.
1.Since the heater is powered by ignition, the voltage must be viewed immediately.
2.The PCM supplies a bias voltage (350 mv to 550 mv) to the sensor. If the sensor is too hot due to converter temp or ignition on too long this voltage could be above 550 mv or below 350 mv.
3.If it has been verified the exhaust is cool at the sensor, and the voltage is above or below the specified value it could be due to leakage current between wires or possible leakage inside the sensor 4-way connector. Wire routing and connector should be carefully inspected.
4.With the engine not running, there should mainly be oxygen inside the exhaust as indicated by the voltage going down. However, depending on the amount of contaminates on the sensor this voltage could go up due to the heater causing this residue to be burned off using up any oxygen around the sensor.
NOTE: Do not apply grease or any material in the H02S-2 connector or alter the wiring in any way. The wires carry air reference to the sensor used to determine the difference in oxygen from the exhaust gas to the PCM.