P0135

CIRCUIT DESCRIPTION
Heated oxygen sensors (HO2S) are used to minimize the amount of time required to enter Closed Loop fuel control operation and to allow accurate catalyst monitoring. The HO2S 1 heater is fed power directly from ignition 1. The HO2S 1 heater control circuit or heater ground is connected to the Powertrain Control Module (PCM). The PCM controls HO2S heater operation by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver for the HO2S 1 heater control circuit has the ability to measure the amount of current drawn by the controlled device.

CONDITIONS FOR RUNNING THE DTC
There are no active DTCs of any of the following types present:
^ DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202-P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set.
^ The ignition voltage is more than 9 volts and less than 18 volts.
^ The engine run time is more than 4 minutes.
^ The engine coolant temperature is more than 70°C (158°F).
^ The engine RPM is between 650-2,500 RPM.
^ The air flow is between 4-26 g/s.

CONDITIONS FOR SETTING THE DTC
The HO2S 1 Heater Current is not within the calibrated range.

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 1-12:

Steps 13-18:

The numbers below refer to the step numbers on the diagnostic table.
2. Check the O2 heater current with the engine at operating temperature, and allow time for the heater current to stabilize. The HO2S heater current is initially higher until the sensor reaches full operating temperature.
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 case the HO2S low reference or HO2S heater low control circuit is malfunctioning.
5. This step checks the HO2S heater ground circuit. The engine must be running for the PCM to enable the heater.