P1161

Circuit Description
The HO2S heater circuit reduces the time required for the oxygen sensor to reach operating temperature and maintains the operating temperature during extended idle periods. When the ignition is turned to the on position, voltage is supplied to the sensor heater from the engine controls power relay through a fuse. The ECM controls the heater operation by first modulating the ground circuit when the sensors are cold, and then turning the heaters on continuously after a predetermined amount of time. This prevents the possibility of thermal shock to the sensor by controlling the sensor's rate of heating. Once the sensor reaches operating temperature, the ECM may again modulate the ground.

Conditions for Running the DTC
^ The battery voltage is greater than 9 volts.
^ The engine is running.
^ The sensor heater is on.

Conditions for Setting the DTC
A fault is detected in the heater control circuit.

Action Taken When the DTC Sets
The Engine Control Module (ECM) illuminates the Malfunction Indicator Lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.

Conditions for Clearing the MIL/DTC
^ The ECM turns off the MIL after 3 consecutive drive trips that the diagnostic runs and passes.
^ A History DTC clears after 40 consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic.
^ The ECM battery voltage is interrupted.
^ The scan tool clears the MIL/DTC.

Diagnostic Aids

Notice: Refer to J 35616-A Connector Test Adapter kit Notice in Service Precautions.

Use the J 35616-A Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

An open fuse in the HO2S heater circuit may be caused by the heater element in one of the sensors. The condition may not be present until the sensor operates for a period of time. If no fault is present in the heater circuit, monitor the amperage of each heater using the DMM to determine if one of the heater elements is the cause of the open fuse.

Check for the following conditions:
^ The sensor pigtail or the harness may be mis-positioned and contacting the exhaust system.
^ An intermittent or poor connection or corrosion in the connector, refer to Intermittents and Poor Connections Diagnosis. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table:
2. Multiple HO2S DTCs will set if the supply voltage to the sensor heaters is open.
9. The test lamp may illuminate or flash depending on the operating conditions. This indicates the ECM and the control circuit are functioning. The engine must be running for the ECM to operate the control circuit.
11. The ECM provides the reference ground for the oxygen sensor. A small amount of current will appear on this circuit when the ECM is operational. The measured resistance of the circuit will increase when the ECM is operational. This is considered normal.