Hi guys I just bought a universal oxygen sensor for my peugeot 306. As it's universal the wires don't match with my car. I've worked out the colours for the sensor. But I don't know the colour of the wires coming from my engine. The colours are red, green yellow and gray. Thanks!

Once I find out which oxygen sensor is bad, I want to try and replace it myself because the dealers won't to charge $500 for the part and the manual labor. The part only cost $70 and I've got time. What tools should I buy to change out the sensor? Pictures or a video would be helpful.

When my check engine light came on, i took the car to autozone for code reading and it read defective oxygen sensor, my mechanic just told me to change the front one, he was not sure which one is defective( there are two of them), how do i know which one is defective to avoid just wasting money?

My service engine light came on today and I plugged my scanner in. It said that the oxygen sensor needs replacement and I was wondering how urgent that is. The car is running just fine but will it eventually lead to some other defect? Is it important that I get it replaced immediately?