P0135

CIRCUIT DESCRIPTION
The Heated Oxygen Sensors (HO2Ss) are used in order to minimize the time required for the closed loop fuel control operation and in order to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the time required for the HO2S 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 Powertrain Control Module (PCM) will run the heater test only after a cold start, as determined by the Engine Coolant Temperature (ECT) and by the Intake Air Temperature (IAT) at the time of start-up, and 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 looks at how much time has elapsed since the start-up. The time needed for the HO2S to reach the operating temperature is based on the engine coolant temperature at start-up and the average Mass Air Flow (MAF) since start-up. A higher average airflow or a higher start-up engine coolant temperature equals a shorter time to HO2S activity. If the PCM determines that too much time was required for the HO2S 1 to become active, DTC P0135 will set.

CONDITIONS FOR RUNNING THE DTC
^ DTCs PO1O1, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set.
^ The engine run time is more than 3 seconds.
^ The system voltage is between 9-16 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 (11°F) of each other at start-up.
^ The average mass airflow for the sample period is less than 21 g/s.

CONDITIONS FOR SETTING THE DTC
The HO2S 1 voltage remains within 150 mV of the bias voltage of approximately 450 mV for a longer amount of time than it should. The amount of time ranges between 50-85 seconds and depends on the engine coolant temperature at start-up and the average mass air flow since start-up.

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 1-10:

Steps 11-17:

The numbers below refer to the step numbers on the diagnostic table.
2. The HO2S should be allowed to cool before you perform 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 the event that the HO2S low signal or HO2S heater ground circuit is malfunctioning.
5. This step tests the HO2S heater ground circuit.
6. This step tests for an open or shorted HO2S heater element.
11. An open HO2S high signal or an open HO2S low signal circuit can cause the DTC to set with the HO2S heater operating normally. Test the HO2S high and low signal circuits before replacing the sensor.