P0141

CIRCUIT DESCRIPTION
Heated oxygen sensors (HO2S) are used in order to minimize the time required for closed loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the time required for fuel control sensor HQ2S 1 to become active. The oxygen sensor heater is required by catalyst monitor sensor HO2S 2 in order to maintain a sufficiently high temperature. This allows accurate exhaust oxygen content readings further from the engine.

The power control module (PCM) will run the heater test only after a cold start, determined by engine coolant temperature and the intake air temperature at the time of startup, and will test only once during an ignition cycle. When the engine is started the PCM will monitor the HO2S voltage. When the HO2S voltage indicates a sufficiently active sensor, the PCM determines how much time has elapsed since startup. If the PCM determines that too much time was required for the HO2S 2 to become active, DTC P0141 will set. The time the HO2S needs to reach the operating temperature is based on the engine coolant temperature at startup and the average mass air flow since start-up. A higher average airflow or higher startup engine coolant temperature means less time to HO2S activity.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202-P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set.
^ The system voltage is 9-18 volts.
^ The Intake Air Temperature (IAT) is less than 35°C (95°F) at start-up.
^ The Engine Coolant Temperature (ECT) is less than 35°C (95°F) at start-up.
^ The IAT and the ECT are within 6°C (42°F) of each other at start-up.

CONDITIONS FOR SETTING THE DTC
HO2S 2 voltage remains within 150 mV of the bias voltage, or approximately 450 mV for a longer period of time than required. The time ranges between 100-130 seconds depending on the engine coolant temperature at startup and the average air flow since startup.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

TEST DESCRIPTION

Steps 1-12:

Steps 13-17:

The numbers below refer to the step numbers on the diagnostic table.
2. The HO2S should be allowed to cool before performing this test. If the HO2S heater is functioning, the signal voltage will gradually increase or decrease as the sensor element warms. If the heater is not functioning, the HO2S signal will remain near the 450 mV bias voltage.
4. This step ensures that the ignition 1 voltage circuit to the HO2S is not open or shorted. The test lamp should be connected to a good chassis ground, in case the HO2S low signal or HO2S heater ground circuit is malfunctioning.
5. Tests the HO2S heater ground circuit.
6. Tests for an open or shorted HO2S heater element.

IMPORTANT: The heater element resistance will vary according to the HO2S temperature. A hot HO2S heater element will measure a much higher resistance than a HO2S heater element at ambient temperature. Allow the HO2S heater element resistance.

11. An open HO2S high or low circuit can cause the DTC to set with a good HO2S signal and the HO2S signal and the HO2S low circuits before replacing the sensor.