Tips to Diagnose an Audi’s Failing 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.

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.

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

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.

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.