Technical Description of OBD-II Trouble Code
Low Voltage in 02 Sensor Circuit (Bank 1 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.
The Catalytic Converter is responsible for controlling emissions. The PCM (Powertrain Control Module) uses the signal from the oxygen sensor located at the rear of the catalyst to monitor the efficiency of the catalyst.
This sensor is located in bank 1, position 3. It is a four-wire sensor that receives a 0.5 volt reference voltage, as well as power and ground circuits for the o2 sensor heater element. There is also a signal wire from the oxygen sensor to the PCM that can vary between approximately 0.1 volts to 0.9 volts depending on the oxygen content of the exhaust. A properly functioning post-cat sensor will exhibit small changes at a slower rate compared to front o2 sensors.
To simplify, the main function of a post-cat sensor is to monitor catalyst efficiency, not control fuel management (although it can have some influence over the operation of the front o2 sensor). If the PCM determines that the post-cat o2 sensor signal voltage remains below a certain threshold for too long, it will set the P0143 code. The PCM detected that the HO2S signal was less than 156 mv for 28 seconds.
Symptoms
Rear o2 sensor problems usually do not cause drivability issues since they are an input that measures catalyst efficiency (unlike front o2 sensors). However, if there are other codes present, such as lean codes or pre-o2 sensor codes, they may cause drivability problems along with P0143. The following symptoms may be present:
Causes
This code can be set if the engine is running lean, although there will likely be other codes present as well.
Possible Solutions
It is always a good idea to start by checking for air leaks in the exhaust manifold and pipes.
With the engine running, use a scan tool or voltmeter to check the o2 sensor signal voltage with the engine warm. You may need to increase the RPM to a fast idle in order to check the voltage of the bank 1, position 3 sensor. If the voltage remains stuck low (less than half a volt) and there are no other o2 sensor codes present in the PCM, then it is likely that the sensor is faulty. If the voltage is not stuck low and the o2 sensor appears to be operating correctly, it may be intermittently sticking low. In many cases, this turns out to be a faulty sensor.
However, if you want to determine the exact problem, follow these steps: 1. Turn off the engine and unplug the connector for the bank 1, position 3 o2 sensor. Make sure that there is battery voltage and ground present for the o2 sensor heater. If not, diagnose and fix that issue first, then retest. If everything checks out, use a jumper wire to supply a chassis ground to the o2 sensor connector (PCM side) ground circuit. Now observe the o2 sensor reading for bank 1, position 3 on the scan tool. If the reading is now around half a volt, replace the o2 sensor. If the voltage reading does not change after supplying a ground to the unplugged PCM side of the o2 sensor connector, check the harness for a short to ground.
Check for any contact between the harness and exhaust components. Inspect the pins for damage and moisture. Repair as necessary. If no harness problems are found, the PCM may be faulty.
