P0161

Diagnostic Chart:

Diagnostic Chart (cont'd):

Wiring Diagram:

Circuit Description
The VCM supplies a voltage of about 0.45V (450 mV) between the HO2S High and the HO2S Low circuits. If the voltage is measured using a 10 megohm digital voltmeter, the voltage may read as low as 0.32V. The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1V (1000 mV) if the exhaust system is rich to as low as 0.10 V (100 mV) if the exhaust is lean.

When HO2S temperature is below 360°C (600°F), the sensor will not produce any voltage and will behave like an open circuit. This will result in Open Loop operation.

The HO2S heater provides for faster sensor warm-up which allows the sensor to become active in a shorter period of time and remain active during long extended idle. DTC P0161 determines if the HO2S heater is functioning properly by monitoring the amount of time necessary for the HO2S to become active after start-up. DTC P0161 is a type B DTC.

Conditions for Setting the DTC

^ System Voltage is greater than 9V but less than 17V.
^ MAF is less than 27 grams per second.
^ Engine Coolant Temperature (ECT) is less than 32°C (90°F).
^ Intake Air Temperature (IAT) is less than 32°C (90°F).
^ The difference between the ECT sensor and the IAC sensor is no more than 5°C (41°F).
^ The time for the HO2S (Bank2 sensor2) to obtain ±150 mV from 450 mV is to great.

Action Taken When the DTC Sets
The VCM will turn ON the Malfunction Indicator Lamp (MIL) after two consecutive test cycles with the fault active.

Conditions for Clearing the MIL/DTC
The VCM turns the MIL off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids
Check for the following:

^ Poor connection or damaged harness. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
^ Never solder the HO2S wires.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.

2. This step determines if DTC P0161 is the result of a hard failure or an intermittent condition. With the ignition ON, engine OFF, the HO2S (Bank 2 Sensor 2) voltage displayed on the scan tool should gradually change 0.150V, indicating that the heater is working properly. HO2S voltage can rise as high as 975 mV before it toggles back down. The main thing to look for is a change.
3. Probing terminal D of the HO2S (Bank 2 Sensor 2) connector verifies if voltage is available to the HO2S (Bank 2 Sensor 2) heater.