P0135

Circuit Description
The PCM supplies a bias voltage (approximately 450 mV) on the Heated Oxygen Sensor (HO2S) signal high and low circuits. When you turn the ignition to the ON position, battery voltage is supplied to the HO2S heater. As the heater reaches the operating temperature, the HO2S voltage responds by changing from a bias voltage range to the normal operation. Typically, as the HO2S reaches the operating temperature, the HO2S voltage goes from a bias voltage to a voltage below 300 mV. Depending on the exhaust gas content, it is possible for the HO2S voltage to go above 450 mV.

The PCM runs the heater test only on a cold start (depends on the cumulative air flow) and only once an ignition cycle. When you start the engine the PCM monitors the HO2S voltage. When the HO2S voltage goes above or below the bias range threshold, the PCM determines how much time it took. If the PCM detects that the process took too much time for the HO2S to enter into normal operating range, a DTC sets. The time the process takes the HO2S to reach operating temperature is based on the amount of air that flows into the engine.

Conditions for Running the DTC
^ DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358, P1258 not set.
^ The intake air temperature and the engine coolant temperature are less than 50°C (122°F) and are within 8°C (14.5°F) of each other at engine start-up.
^ The ignition voltage is between 10.0 volts and 18.0 volts.
^ The AIR, EGR, and the Catalyst diagnostics are not active.

Conditions for Setting the DTC
The HO2S voltage remains between 300 mV and 700 mV for a predetermined amount of time (depends on engine coolant temperature and air flow).

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp 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 the MIL OFF after three consecutive ignition cycles that the diagnostic runs and does not fail.
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

^ Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For an intermittent condition, refer to Symptoms. Symptom Related Diagnostic Procedures
^ The heater diagnostic will only run on a cold start and run once per ignition cycle.
^ An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provides the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. Allow the engine to cool before performing this test. If the sensor is at the operating temperature the HO2S voltage will stay high or low. If the HO2S voltage stays between 300-700 mV indicates the HO2S heater is inoperative. For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter kit J 35616-A. Using this kit will prevent damage to the harness connector terminals.
3. If more than one HO2S DTC is set, this is a good indication that the HO2S fuse is open. Test all the related circuits going to all the heated oxygen sensors for a short to ground. If you cannot locate a shorted circuit, it may be necessary to disconnect each HO2S one at a time to locate a shorted sensor.
4. This step tests whether a B+ supply is available at the sensor.
5. This step tests whether a ground is available at the sensor.
6. This step tests whether the HO2S heater element is internally open.
7. Inspect the ignition feed circuits at the Underhood Electrical Center for poor connections. Refer to Intermittents and Poor Connections Diagnosis.
8. Test the ground circuits for an open if more then one heater DTC sets. Intermittent Conditions