Technical Description of OBD-II Trouble Code
Slow Response in O2 Sensor Circuit (Bank 1 Sensor 3)
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all vehicles manufactured from 1996 onwards (such as Mitsubishi, Nissan, Volkswagen, Inifiniti, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
If your OBD-II equipped vehicle has a stored P0145 code, it means that the powertrain control module (PCM) has detected a slow response time from a downstream oxygen (O2) sensor or circuit located after the catalytic converter. Bank 1 refers to the engine bank that contains the number one cylinder, and Sensor 3 indicates that the issue is related to the downstream sensor in a system equipped with only three sensors (as opposed to a four-sensor system).
O2 sensors are made up of a zirconium dioxide sensing element that is protected by a vented steel housing. The sensing element is connected to wire leads in the O2 sensor wiring harness using platinum electrodes. The PCM is connected to the O2 sensor wiring harness using the controller area network (CAN). The O2 sensor supplies the PCM with data about the percentage of oxygen particles in the engine exhaust compared to the oxygen content of the ambient air.
Exhaust gases flow through the exhaust pipe and pass through the catalytic converter before reaching the downstream O2 sensor. As the exhaust flows through vent holes in the steel housing and across the sensing element, ambient air is drawn into a small chamber in the middle of the sensor through the wire lead cavities. The ambient air in the chamber is heated by the exhaust, causing the oxygen ions to produce voltage. Changes in the number of oxygen molecules in the ambient air drawn into the O2 sensor compared to the concentration of oxygen ions in the exhaust gases cause the voltage to change. These voltage changes cause the oxygen ions inside the O2 sensor to rapidly and repeatedly jump between platinum layers.
Voltage variations occur as the rushing oxygen ions jump between platinum layers. The PCM identifies these voltage variations as changes in exhaust oxygen concentration, which indicate whether the engine is running lean (too little fuel) or rich (too much fuel). The voltage signal from the O2 sensor is low when there is more oxygen present in the exhaust (lean condition) and high when there is less oxygen present in the exhaust (rich condition). The PCM primarily uses this data to monitor the efficiency of the catalytic converter. If the downstream O2 sensor circuit fails to cycle as expected over a set period of time and under certain programmed circumstances, a P0145 code will be stored and the malfunction indicator lamp may illuminate.
Severity & Symptoms
Since a P0145 code indicates that the post catalytic converter O2 sensor has remained slow or unresponsive, it should be addressed as soon as possible.
Symptoms of a P0145 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
When diagnosing a code P0145, you will need a diagnostic scanner, digital volt ohmmeter (DVOM), and a reliable source of vehicle information.
Before attempting to diagnose a P0145 code, any misfire codes, throttle position sensor codes, manifold air pressure code, and mass air flow sensor codes must be diagnosed and repaired. If the engine is not running efficiently, a successful diagnosis cannot be achieved.
Most skilled technicians begin by visually inspecting system wiring harnesses and connectors. Focus on harnesses that are routed near hot exhaust pipes and manifolds, as well as those that are routed near sharp edges like the ones found on exhaust shields.
Connect the scanner to the vehicle diagnostic port to retrieve all stored trouble codes and freeze frame data. Write down this information as it may be helpful if the P0145 code proves to be intermittent. Clear the codes and see if the P0145 is reset.
If the P0145 is reset, start the engine and let it idle (with the transmission in neutral or park) after allowing it to reach normal operating temperature. Observe the O2 sensor input data on the scanner data stream. By narrowing the data stream display to include only pertinent data, you can obtain a more accurate data response. If the engine is running efficiently, the downstream O2 sensor data should reach a mid-line and only fluctuate slightly. If there is little or no fluctuation, a P0145 code will be stored.
To monitor live data from the O2 sensor, connect the DVOM test leads to the sensor ground and signal wires. The DVOM can also be used to check the resistance, voltage, and ground signals of the O2 sensor in question. Disconnect related controllers before testing the system circuit resistance with the DVOM.
Additional diagnostic notes:
