P0135

CIRCUIT DESCRIPTION
Heated Oxygen Sensors (HO2S) are used to minimize the amount of time required for closed loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the amount of time required for fuel control sensor HO2S 1 to become active. The oxygen sensor heater is required by catalyst monitor sensor HO2S 2 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 (determined by engine coolant and intake air temperature at the time of startup) 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 startup. If the PCM determines that too much time was required for the HO2S 1 to become active, a DTC P0135 will set. The time it should take the HO2S to reach operating temperature is based on the engine coolant temperature at start-up and the average mass air flow since startup (higher average airflow or higher startup engine coolant temperature 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.
^ System voltage is between 9-16 volts
^ Intake Air Temperature (IAT) is less than (35°F) at startup
^ Engine Coolant Temperature (ECT) is less than (35°F) at startup
^ IAT and ECT are within 6°C (11°F) of each other at start-up
^ Average mass airflow for the sample period is less than 20 g/s

CONDITIONS FOR SETTING THE DTC
HO2S 1 voltage remains within 150 mV of the bias voltage (about 450 mV) for a longer amount of time than it should. The amount of time ranges between 50-80 seconds depending on engine coolant temperature at startup and average mass air flow since startup.

ACTION TAKEN WHEN THE DTC SETS
^ First failure:
- The MIL is not turned ON.
- A DTC is stored in memory under Failed Last Test.
- The Failure Records are stored.
^ Second consecutive drive cycle with a failure:
- The MIL is turned ON.
- A DTC is stored in memory under history.
- The Freeze Frame data is stored.
- The Failure Records are stored.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after the third consecutive trip the diagnostic has run and passed.
^ The history DTC will clear if the fault conditions have not been detected for 40 warm-up cycles.
^ A scan tool can be used to clear DTC information.

TEST DESCRIPTION

Steps 1-9:

Steps 10-17:

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 ground, in case the HO2S low signal or HO2S heater ground circuit is malfunctioning.
5. This step checks the HO2S heater ground circuit.
6. This step checks for an open or shorted HO2S heater element.
11. An open HO2S high signal or low signal circuit can cause the DTC to set with the HO2S heater operating normally. Check the HO2S high signal and the HO2S low signal circuits before replacing the sensor.