YEOFLAG Audi A3 Oxygen Sensor
What is an Oxygen Sensor
What is an Oxygen Sensor?
A: An emission control component that senses the presence of oxygen in the exhaust stream.
Why is an Oxygen Sensor needed?
A: Vehicles are one of the leading causes of air pollution in the world. As a result, government legislation has enacted regulations in many parts of the world to reduce vehicle emissions and increase fuel efficiency. By more closely controlling a vehicle’s air-fuel ratio, fuel efficiency can be increased, while tailpipe emissions are reduced. The oxygen sensor functions as the eyes and ears for the ECU. Its role is to communicate with the ECU whether a vehicle is running rich or lean. The goal is to have the engine run close to 14.7 parts of air to 1 part of fuel. 14.7:1 is known as the Stoichiometric Point. At this point, optimum combustion under normal conditions occurs and the least amount of harmful gases are produced.
How does an Oxygen Sensor work
Q: How does an Oxygen Sensor work?
A: The sensor becomes operational at approximately 350°C (650″F).
- At this point, a chemical reaction occurs producing a high or low voltage based upon high or low levels of oxygen in the exhaust stream.
- The oxygen sensor generates 800-1000 mV when the exhaust gas air/fuel ratio is rich. It will generate 100-200 mV when the exhaust gas air/fuel ratio is lean.
Output Voltage vs. AFR
Does my vehicle have an Oxygen Sensor?
- A: Most vehicles produced for the North American market after 1981 have at least one oxygen sensor.
- EPA laws required the introduction of oxygen sensors to decrease vehicle tailpipe emissions and improve fuel efficiency.
Oxygen Sensors located
Q: Where are Oxygen Sensors located?
- A: Vehicles produced before 1996 (OBDI) will have one or two sensors upstream of the three-way catalyst (catalytic converter). Vehicles produced after the 1995 model year (OBDIl) will have oxygen sensors both upstream and downstream of the three- way catalyst.
- To explain the sensor locations as found on a scan tool, you must first find the #1 cylinder location. Bank one (1) will always be the side of the engine with the #1 cylinder. Sensor one (1) will always be upstream of the three-way catalyst, while sensor two (2) will be downstream.
- To determine left and right, as this is how the sensors are catalogued, you must first establish the front and rear of an engine.
- The front will be the side of the engine with accessory drive belts for alternators, air conditioning, power steering, etc.
- The left side of the engine will be the side to the left of the accessory drive belts when standing behind the engine. The right side of the engine will be the side to the right of the accessory drive belts when standing behind the engine.
Q: Where are Oxygen Sensors located?
Open Loop and Closed Loop modes
Q: What are “Open Loop” and “Closed Loop” modes?
A: Open-loop mode is the time before the oxygen sensor becomes operational, usually at vehicle start-up. It is also the default mode should a sensor problem occur.
Closed loop mode is the desired mode where the oxygen sensor is operational. At this time AFR and exhaust emissions are being controlled.
Different types of Oxygen Sensors
Q: What are the different types of Oxygen Sensors?
- A: Zirconia
- Most popular (90% of the market)
- 1-4 wire configuration
- Heated or unheated
- Thimble or planar-type
- 18mm thread size
- Requires reference air
- wire (unheated sensor)
- Signal wire
- Ground achieved through sensor body (earth ground)
- wire (unheated sensor)
- Signal wire
- Ground wire (ground achieved through case or isolated ground)
- wire (heated sensor)
- Signal wire
- Ground achieved through sensor body (earth ground)
- Two heater wires
- wire (heated sensor)
- Signal wire
- Ground wire (ground achieved through case or isolated ground)
- Two heater wires
Q: What are the obvious signs and impact of worn Oxygen Sensors?
A: The most obvious sign an oxygen sensor is failing or has failed is a check engine light. Vehicles are designed to inform the driver if there is a problem with the emissions system. A check engine light may point to a problem with the emissions system but does not necessarily mean the oxygen sensor is faulty.
Other signs of worn oxygen sensors are increased fuel consumption and an increase in vehicle emissions.
Q: How can I check my Oxygen Sensors to ensure they are working properly?
- A: There are three (3) ways a sensor can be checked to see if it is functioning properly.
- A professional repair shop will have scan tools to check sensor operation.
- Advanced shops may have a tool called an oscilloscope. This tool will graphically display oxygen sensor output as it switches voltage from high to low.
- Removed from the vehicle, an oxygen sensor can be checked using a common multi-meter to check for heater resistance. In the case of a faulty heater element, the resistance will read as an open circuit.
Shorten the life of an Oxvaen Sensor
Q: What can shorten the life of an Oxvaen Sensor?
A: Common causes for oxygen sensor failure are poisoning from substances such as engine coolant, silicone gasket materials or soot.
- Often these problems can point to other mechanical issues with an engine.
- Thermal shock from raw fuel or moisture in the exhaust can also cause a sensor heater element to crack.
- The root cause of the problem should be addressed along with the replacement of the oxygen sensor if needed.
Install an Oxygen Sensor
Q: How do I install an Oxygen Sensor?
A: Sensor installation will first require the proper tools. A specialty oxygen sensor socket is recommended for removal of the old sensor and installation of a new sensor.
- Disconnect the battery.
- Disconnect the wiring harness from the old sensor.
- Remove any hardware or clips if applicable.
- Use the oxygen sensor socket (shown below) to remove the old sensor.
- Apply anti-seize compound to the threads of the sensor (if not already pre-applied).
- Use a specialty socket to install the new sensor to the recommended torque.
- Put in place any hardware or clips if applicable.
- Connect the wiring of the new sensor to the existing vehicle wiring.
- Reconnect the battery.
Q: What is the expanded role an Oxygen Sensor plays in OBDII vs. OBDI ?
A: In OBDIl-equipped vehicles, there is a sensor downstream of the three-way catalyst to monitor catalyst function and can also assist in controlling AFR by adjusting fuel trim.
- If a catalyst has failed or there is a problem elsewhere in the system, the downstream sensor may trigger a MIL light or check engine light to warn of a possible problem.
- In OBDIl, the ECU is also monitoring the condition of the sensor signal response time, heater light-off time and heater resistance.
Troubleshooting
Common Trouble Codes That Require Replacement Of Oxygen Sensor
Documents / Resources
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YEOFLAG Audi A3 Oxygen Sensor [pdf] User Manual Audi A3 Oxygen Sensor, Audi A3, Oxygen Sensor, Sensor |
