2000 Volvo S80 regular engine, 130k miles. Check engine light illuminates, and a scanner shows the code P0155 - a Oygen Sensor. Clear the code and light - comes back within a few miles of operation. Car runs fine - no stumbling, stalling, etc.

What are my options?

If replacement of the sensor, I was told that there are 4 of them on the car - how do I determine which one and where it physically is located?

Does it screw in and have a plug for the wiring, or is there more to changing it?

And is there a perticular replacement brand I should use or stay away from?

Thanks!!!

There should be more to the code, such as bank number. This is crucial to determine which sensor it is.

Keep in mind, the sensor is just detecting a fault, it could be the sensor, or it could be something else causing the sensor to trip a fault (ie. bad pre-cat or catalytic converter).

In regards to the design, they screw into the exhaust and have a pig tail wire. There is a special socket that is used to remove and reinstall, it has a slot for the pig tail wire to slide through. The problem that happens most often with removing the sensors is they get seized to the exhaust and if you're not careful they will strip the threads.

It could be connection problems as well. Don't just replace the o2 assuming that it's bad. Make sure not to put any type of electrical greese on the connection to any o2 sensor as it will mess them up, as well as anti-sieze(very limited ammount, if any).

Find out what bank (one or two ((or left or right exhaust)) the o2 sensor code is on, (codes read by dealer will tell you this). Disregard whether it is a front or rear o2 sensor fault at this time. Get the codes erased.
Swap the rear sensors with each other then test by using the car till engine light comes back on. Get codes read.

If the code is the same as the original code then the front o2 sensor is required on the bank (exhaust side) that the original code pointed to.

However if the code read is different now and points to the other bank from the original code the rear o2 sensor is required on that bank.

To sum up, basically the code will be on whatever bank the bad o2 sensor is on, so if you swap the rear o2 sensors you will know whether it is the front or rear o2 sensor at fault by watching if the code switches banks.

:thumbsup:

ps; stay away from cheap o2 sensors on volvo`s, will ony cause problems.