Technical Description of OBD-II Trouble Code
Low Voltage in O2 Sensor Circuit (Bank 2 Sensor 3)
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
This code indicates a fault in one of the post-catalyst O2 sensors on Bank 2. The purpose of this oxygen sensor is to monitor the efficiency of the catalytic converter by comparing it to the O2 sensors in front of the catalyst. If the PCM detects little or no difference between the exhaust quality in the post- and pre-catalyst sensors, it indicates that the catalyst is not functioning properly.
In simpler terms, the main job of a post-cat sensor is to monitor catalyst efficiency, not control fuel management. A P0163 code does not necessarily mean that the catalyst is faulty. It indicates that the signal voltage of Bank 2, Sensor 3 is below the normal range for that sensor. This sensor is a four-wire sensor supplied with a 0.5 volt reference voltage on the signal wire, as well as a ground and power circuit for the o2 sensor heater element. Changes in oxygen content cause resistance changes inside the sensor, which affect the 0.5 volts on the signal/reference circuit.
A properly functioning post-catalyst sensor will exhibit small changes at a slower rate compared to front (pre-catalyst) O2 sensors. It may switch slightly above and below 0.45 volts at a rate of about 1 switch per second or less. The PCM monitors this signal change to determine the proper functioning of the catalyst. If the PCM determines that the signal voltage of Bank 2, Sensor 3 remains below a certain threshold for too long, it will set the P0163 code.
Symptoms
Rear O2 sensor problems usually do not cause drivability issues since they measure catalyst efficiency (unlike front O2 sensors). However, if other codes such as lean codes or pre-O2 sensor codes are present, they may cause drivability problems. The following symptoms may be observed:
Causes
Possible causes of a P0163 code include:
Possible Solutions
It is recommended to start by checking for air leaks in the exhaust manifold and pipes. Fix any leaks found. With the engine running, use a scan tool or voltmeter to check the O2 sensor signal voltage of Bank 2, Sensor 3. You may need to increase the RPM to a fast idle to check the voltage. If the voltage remains low (less than 0.5 volts) and there are no other O2 sensor codes present in the PCM, the sensor is likely faulty. If the voltage is not consistently low and the O2 sensor appears to be operating fine, it may be intermittently sticking low. In either case, replacing the sensor can be an effective diagnostic step, although it can be costly if the issue turns out to be a wiring problem rather than a faulty sensor.
If you want to determine the problem before spending unnecessarily, follow these steps: 1. Turn off the engine and unplug the connector of the Bank 2, Sensor 3 O2 sensor. Inspect for corrosion or damage and repair as necessary. Ensure that there is battery voltage and ground present for the O2 sensor heater. If not, diagnose and address that issue first, then retest. The O2 sensor relies on the heater to warm up quickly and start functioning. If the heater element is faulty or not receiving the proper voltage, it may trigger this code. Heater problems usually have associated codes as well. If there is no battery voltage supplying the O2 sensor, use the associated code to diagnose that issue. If the heater element is found to be faulty, replace the sensor. If the heater element is functioning properly, use a jumper wire to supply a chassis ground to the O2 sensor connector’s ground circuit (PCM side). Observe the scan tool’s reading for Bank 2, Sensor 3 O2 sensor. If the reading is now around half a volt, replace the O2 sensor.
If, after supplying a ground to the unplugged PCM side of the O2 sensor connector, the voltage reading does not change, check the harness for a short to ground. Check for any contact between the harness and exhaust components. Inspect the pins for damage or moisture. Repair as necessary. If no issues are found with the harness, the PCM may be at fault.
