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 about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The HO2S 1 heater performance diagnostic will only run from a cold start and only once per key cycle. This DTC will set if the HO2S 1 heater takes too long to heat based on the HO2S 1 signal voltage input to the PCM. The HO2S 1 heater circuit is energized anytime the ignition key is in the ON position. If the PCM detects that the HO2S 1 heater takes too long to heat, based on the HO2S 1 signal voltage, DTC P0135 will set. The HO2S 1 has the following circuits:
- HO2S 1 high signal
- HO2S 1 low signal
- HO2S 1 heater ignition 1 voltage
- HO2S 1 heater ground

CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, 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 intake air temperature (IAT) and the engine coolant temperature (ECT) are within 6°C (11°F) of each other at start-up.
- The HO2S 1 parameter must be between 400-500 mV at start-up.
- The system voltage is between 9-18 volts.

CONDITIONS FOR SETTING THE DTC
The PCM detects that the HO2S 1 voltage remains within 150 mV of the bias voltage, about 450 mV, for a longer amount of time than necessary. The amount of time ranges between 50-80 seconds depending on ECT at startup and average MAF since startup.

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 4-5:

Steps 6-10:

Steps 11-14:

The numbers below refer to the step numbers on the diagnostic table.
2. The HO2S 1 should be allowed to cool before performing this test. The HO2S 1 is cool enough if the voltage output is stable at bias or, about 450 mV. If the HO2S 1 heater is functioning, the signal voltage will gradually change as the sensor element warms. If the heater is not functioning, the HO2S 1 signal will remain near the 450 mV bias voltage.
4. This step ensures that the ignition 1 voltage circuit to the HO2S 1 is not open or shorted. The test lamp must be connected to a good ground, independent of the HO2S system.
6. This test must not be performed until the HO2S 1 heater has cooled and stabilized for at least 15 minutes. Heater resistance is typically about 5 ohms at room temperature.