P0135

CIRCUIT DESCRIPTION
Heating elements inside the heated oxygen sensors (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The HO2S heater operation is controlled by the powertrain control module (PCM). A high side driver supplies ignition power to the bank 1 HO2S 1, and is equipped with a current monitor. Two low side drivers provide the heater ground path. The bank 2 HO2S 1 is supplied power from the external ignition 1 voltage circuit, and uses the same low side drivers. When the ignition switch is turned ON the PCM performs an HO2S heater circuit check using the high side driver current monitor circuit. When the engine is started, all three drivers are switched ON. One of the low drivers is for heater warm-up only, and is used until the proper heater temperature is reached. When the warm-up low driver is switched OFF, the heater ground path is controlled through the remaining low side driver. The PCM now records the total heater circuit current, if the heater current remains stable the PCM momentarily turns OFF the high side driver. The PCM now records the bank 2 HO2S 1 current. This value is subtracted from the previously recorded total and is used to determine the condition of the heater circuit. If the PCM detects a HO2S bank 1 sensor 1 heater current outside of the calibrated range, DTC P0135 will set.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0030, P1031, P1032 are not set.
- The Engine Speed parameter is between 500-3,000 RPM.
- The Engine Run Time parameter is more than 3 minutes.
- The MAF parameter is between 4-30 g/s.
- All of the above conditions are met for 3 seconds.

CONDITIONS FOR SETTING THE DTC
The PCM detects an HO2S bank 1 sensor 1 heater current value outside 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.
- Clear the MIL and the DTC with a scan tool.

TEST

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