P0135

CIRCUIT DESCRIPTION
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of 450 mV. The HO2S generates a voltage within a range of 0-1000 mV, that fluctuates above and below bias voltage once in Closed Loop. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. A heating element inside the HO2S reduces the time required for the sensor to reach operating temperature, and provide an accurate voltage signal.

The HO2S heater diagnostic runs continuously when the heater circuit is energized. The HO2S heater circuit is only energized when the engine is running or commanded ON by the scan tool. The DTC will set if the heater current is above or below a calibrated threshold for 200 seconds.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0201, P0202, P0203, P0204, P0300, P0301 - P0304, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P1441, or P1621 are not set.
^ The ignition 1 signal is between 10-16.5 volts.
^ The engine coolant temperature (ECT) is more than 70°C (158°F).
^ The air flow calculated is less than 16 g/s.
^ The fuel level sensor is more than 10 percent.
^ The engine run time is more than 60 seconds.

CONDITIONS FOR SETTING THE DTC
The HO2S 1 heater current is not within the calibrated range for more than 200 seconds.

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

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
^ 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 1-8:

Steps 9-15:

The numbers below refer to the step numbers on the diagnostic table.
2. Allowing the engine to cool before performing this test allows the HO2S 1 to cool which causes the HO2S signal voltage to return to near bias voltage, approximately 450 mV. After the HO2S 1 heater is commanded ON, the HO2S will heat up. This will cause the signal voltage to change either more than or less than bias voltage, verifying the HO2S 1 heater is operating.
4. Tests for voltage at the HO2S 1 heater. The oxygen sensor (O2) fuse supplies power to the HO2S 1 heater.
5. This test verifies that the PCM is providing ground to the HO2S 1 heater.
6. This step tests if ground is constantly being applied to the HO2S 1 heater.