Tips to Diagnose an Audi’s Failing Oxygen Sensor

One of the most important parts of your Audi is the oxygen sensor, or O2 sensor. This integral component is actually often overlooked by drivers. Without a working O2 sensor, your Audi’s entire engine system will be out of sync, meaning you will notice a drop in performance along with increased fuel consumption. Let’s take a closer look at how to avoid these worrying symptoms and how to diagnose a failing oxygen sensor in your Audi quickly.

The Purpose of the Oxygen Sensor

Your Audi’s main onboard computer the engine control unit (ECU) needs to know the composition of the exhaust gases to work out if the fuel levels, fuel timing, and fuel delivery is accurate. To do this, it relies upon the O2 sensor. This is mounted within the exhaust system. There are typically two sensors used. One is in the exhaust manifold and the other is near the catalytic converter.

The O2 sensor is responsible for measuring the proportion of oxygen inside the exhaust gases. It then compares to the ambient air and transfers the data to the ECU.

Common Causes of O2 Sensor Failure

The most common cause of O2 sensor failure is contamination, as they can often become covered with various engine deposits. You can often inspect your O2 sensor to figure out what has caused it to fail. There are four common types of O2 sensor contamination that will all appear differently on the unit:

• Orange/Rusty Corrosion: The O2 sensor has become contaminated by lead.
• Patches of White: The O2 sensor is contaminated by coolant/antifreeze.
• Dark in Color: The O2 sensor has been contaminated by a rich fuel mixture.
• Completely White: The O2 sensor has been contaminated by silicone sealant.

Aside from contamination, the O2 sensor can also fail because the element has become old and worn down. This will cause the part to lag and then completely fail, at which point it will need replacement. Sometimes the ECU will pick up on a failing O2 sensor and will note when the voltage readings are outside normal parameters. It will send an error code to the fault memory and illuminate the check engine light. A mechanic can use a diagnostic tool to translate these codes and locate the cause of the problem to make the repair.

Symptoms of O2 Sensor Failure

Many of the symptoms of O2 failure can be similar to those of other part failure. This means that the trouble code produced by the ECU can be pivotal to diagnosing O2 sensor problems. However, if you notice any of the symptoms listed below, you’ll probably want to bring your Audi to an experienced auto shop for diagnostic repairs.

• low gas mileage
• power loss
• black emissions
• failed emissions test
• rough idling
• engine hesitation or stalling

Replacing the O2 Sensor

When it comes time to replace the O2 sensor, you have one of two options. With some know how and some tools, you can attempt to replace the sensor at home. This is usually a straight forward job for those with some DIY skills. It is worth noting that depending on your model of Audi, accessing the O2 sensor can be tricky and you may need to disassemble or remove some parts to reach it.

The second issue you might find if you decide to replace the O2 sensor at home is that the part has to go through many cycles of heating up and cooling down in its life span, which means that its threads will often seize, which can make removal difficult. Auto techs will tend to resolve this issue using heat.

You’ll also need to bare in mind that DIY repairs can be expensive, and in fact, it can cost more than paying for professional servicing, as it will often take you far longer and require the purchase of special tools on top of the cost of the part as well.

Take the Stress Out of O2 Sensor Repair With Professional Automotive

At Professional Automotive, we strive to take the stress out of auto repair and servicing. We are based in Marlborough, MA and have been helping the local community with automotive repairs and maintenance over 22 years. We pride ourself on our honesty and will always be completely transparent when discussing the work your Audi needs done. We’ll never sting you with extra costs. With our 2-year/24,000-mile warranty, you can drive away with complete peace of mind.