P0161

DTC P0161

CIRCUIT DESCRIPTION
The DTC P0141 Heated Oxygen Sensor (HO2S) Heater Performance Bank 1 Sensor 2 diagnostic monitors the operation of the HO2S 2 heater circuit. The DTC P0161 HO2S Heater Performance Bank 2 Sensor 2 diagnostic monitors the operation of the HO2S 2 heater circuit. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. A low side driver within the powertrain control module (PCM) is pulse width controlled to provide current to the heater elements. During warm-up the PCM will pulse the heaters ON-OFF to prevent thermal shock to the sensor components from moisture in the exhaust system. The PCM will not allow continuous HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The PCM continuously monitors the HO2S heater current draw and operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low, 2.6-4.6 volts. When the low side driver is commanded OFF, the reference voltage is high, close to battery voltage. The PCM calculates the HO2S heater element resistance based on the actual heater current. If the PCM detects that the HO2S heater element resistance is too high, this DTC will set.

Each HO2S has the following circuits:
- HO2S high signal
- HO2S low signal
- HO2S heater ignition 1 voltage
- HO2S heater low control

DTC DESCRIPTOR
This diagnostic procedure supports the following DTCs.
- DTC P0141 HO2S Heater Performance Bank 1 Sensor 2
- DTC P0161 HO2S Heater Performance Bank 2 Sensor 2

CONDITIONS FOR RUNNING THE DTC
- The engine is operating.
- The ignition 1 voltage is more than 10.5 volts.
- The HO2S 2 heaters are commanded ON.
- DTCs P0141 and P0161 run continuously once the above conditions are met.

CONDITIONS FOR SETTING THE DTC
- The PCM detects that the affected HO2S 2 Heater Current is not within the expected range.
- The condition exists for more than 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
- 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 1-9:

Steps 10-13:

The number below refers to the step number on the diagnostic table.
4. This test must not be performed until the HO2S heater has cooled and stabilized for at least 15 minutes. Heater resistance is typically about 10 ohms at room temperature.
5. This step tests for high resistance in the ignition 1 voltage circuit of the HO2S 2. If the DMM does not display near battery voltage, repair the high resistance in the ignition 1 voltage circuit.