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Audi A3/A4 B7: How to Replace Oxygen Sensor

The O2 sensor is an important part of maintaining the fuel efficiency of your car. This article details how you can replace a failed O2 sensor.

By Jared Hammond - March 24, 2016

This article applies to the Audi A3 and A4 B7 (1996-2008).

Have you noticed your fuel efficiency has been going down? Is your engine not running like it used to? It's possible that you have a problem with the O2 sensor. The O2 sensor measures the air/fuel mixture leaving your engine and helps calculate how much more air and fuel your engine needs. Without it, you'll find that your fuel efficiency goes down and your engine won't be running at its maximum potential. You can go without a working O2 sensor for a long time, but it's something that's definitely worth fixing.

Audi A3/A4 B7: How to Replace Oxygen Sensor

Materials Needed

  • Replacement O2 sensor
  • Ratchet with O2 sensor socket and extension
  • Ross-Tech VAG-COM (optional)
  • Anti-seize

Before you replace the O2 sensor, you'll need to figure out which one needs to be replaced. The 2.0t engine utilizes two oxygen sensors: one in the exhaust manifold and one downstream, after the secondary catalytic converter. These are referred to as "Bank 1" and "Bank 2" sensors, respectively.

Step 1 – Remove the old O2 sensor

Locate the problematic O2 sensor. You'll see it sticking out from the exhaust with a long wiring harness connected to it. Start by following the harness to the electrical plug and disconnecting it. You'll usually find the plugs mounted near the firewall. Then attach your O2 sensor socket to a ratchet. Fit the socket around the O2 sensor and unscrew the sensor from the exhaust.

It's really that simple. The trouble with it is that it's tricky to remove the sensor from the exhaust because there's not much room to work in. If you're replacing the Bank 1 sensor, you should be able to reach it from the engine compartment using an extension. On the Audi A4 you may need to remove the air filter box to reach it. The Bank 2 sensor, on the other hand, is much harder to reach. You may want to lift the car and approach the sensor from below.

  • AUDI A3 A4 B7 B8 O2 OXYGEN LAMBDA SENSOR REPLACE REMOVE CHANGE HOW TO
    Figure 1. Bank 1 sensor is easily accessible from the engine bay.
  • AUDI A3 A4 B7 B8 O2 OXYGEN LAMBDA SENSOR REPLACE REMOVE CHANGE HOW TO
    Figure 2. Disconnect the O2 sensor plug.
  • AUDI A3 A4 B7 B8 O2 OXYGEN LAMBDA SENSOR REPLACE REMOVE CHANGE HOW TO
    Figure 3. Remove O2 sensor from exhaust.

Pro Tip

O2 Sensors can often get stuck or seize inside the manifolds due to heat cycling. Spray the sensors with penetrating oil a few times in the days before attempting this to help combat this issue. Additionally, if you are already too deep into this, and want to get the job done, quickly blasting the O2 sensor and manifold with an Oxi-Acetylene torch can help. These can be purchased for about $20 at your local hardware store.

Step 2 – Install new O2 sensor

Make sure that you have the correct type of sensor. Applying a small amount of anti-seize grease will make the O2 sensor easier to remove in the future. Thread in the new O2 sensor by hand, then tighten it with a ratchet. Then reconnect the electrical connector. It will take some time for the computer to adjust to the new sensor, so don't expect your trouble codes to get cleared right away. But it should stop after driving the car for a while.

Pro Tip

If you're installing a universal O2 sensor, you'll also need to cut off the plug from the old sensor and solder the wires of the new sensor to the plug.

Featured Video: Audi A4 O2 Lambda Sensor Replacement

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