P0135

CIRCUIT DESCRIPTION
Heated oxygen sensors (HO2S) are used in order to minimize the amount of time required for Closed Loop fuel control operation and to allow accurate catalyst monitoring. The Oxygen Sensor (O2S) heater greatly decreases the amount of time required for fuel control sensors to become active. An O2S heater is also required by catalyst monitor sensor to maintain a sufficiently high temperature which 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, and only once during an ignition cycle. A cold start is determined by Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) at the time of startup. 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 startup. If the PCM determines that too much time was required for the HO2S to become active, this Diagnostic Trouble Code (DTC) will set. The time for the HO2S to reach operating temperature is based on the ECT at start-up and the average Mass Air Flow (MAF) since startup. The higher average airflow, or the higher startup ECT equals a shorter 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-P0206, P0410, P0440, P0442, P0443, P0446, P0449 or P1441 are not set.
^ The Intake Air Temperature (IAT) is less than 35°C (95°F) at startup
^ The Engine Coolant Temperature (ECT) is less than 35°C (95°F) at startup.
^ The IAT and the ECT are within 6°C (11°F) of each other at start-up.
^ The average mass air flow for the sample period is less than 20 g/s.
^ The system voltage is between 9-18 volts.

CONDITIONS FOR SETTING THE DTC
The HO2S voltage remains within 150 mV of the bias voltage (about 450 mV) for a longer time than normal. The amount of time ranges between 42 seconds and 2 minutes.

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.

DIAGNOSTIC AIDS
If the condition is intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-12:

Steps 13-15:

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 ground, in case the HO2S low signal or HO2S heater ground circuit is poor.
5. This step tests the HO2S heater ground circuit.
6. This step checks for an open or shorted HO2S heater element. The heater element resistance will vary according to HO2S temperature. A hot HO2S heater element will measure a much higher resistance than a HO2S heater element at room temperature. Allow the HO2S to cool before measuring HO2S heater element resistance.