P0141

CIRCUIT DESCRIPTION
Heating elements inside the heated oxygen sensors (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal, the HO2S heater operation is controlled by the powertrain control module (PCM). The HO2S 2 is supplied power from the external ignition 1 voltage circuit. The PCM controls the HO2S 2 heater low control circuit with a low side driver. The HO2S 2 heater diagnostic monitors the current draw through the low side driver when the engine is running. The HO2S 2 heater diagnostic will run only after a cold start. To determine if the engine has been started from cold the PCM compares the engine coolant temperature (ECT) at key ON to that at the last key OFF. The ECT difference and the average mass air flow (MAF) since start-up determines how much time that the HO2S 2 should take to produce an active voltage signal. If the PCM detects an HO2S 2 voltage signal with a slower than expected time to activity, P0141 will set.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0137, P0138, P0140 are not set.
- The PCM has determined the current ignition cycle is a cold start.
- The system voltage is between 10-18 volts.
- The average MAF is less than 30 grams per second.
- The HO2S Bank 1 Sensor 2 voltage parameter is between 360-540 mV at start-up.

CONDITIONS FOR SETTING THE DTC
The PCM detects that the HO2S 2 voltage remains within 150 mV of the bias voltage for a longer amount of time than expected.

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.
- Clear the MIL and the DTC with a scan tool.

TEST DESCRIPTION

Steps 1-3:

Steps 4-6:

Steps 7-10:

Steps 11-15:

The number below refers to the step number on the diagnostic table.
3. The HO2S 2 should be allowed to cool before performing this test. The HO2S 2 is cool enough if the voltage output is stable at bias or, about 450 mV. If the HO2S 2 heater is functioning, the signal voltage will gradually decrease as the sensor element warms. If the heater is not functioning, the HO2S 2 signal will remain near the 450 mV bias voltage.