Oxygen Sensor

[belfastmark]

Hi Folks
My engine light lit up on Friday, took it to my mechanic and had a fault read done which showed up a problem with the Oxygen Sensor. Have one ordered and the car is booked in for Tuesday. Since then, I have discovered that there are two Oxygen Sensors in the car. One is before the Cat and one is after the Cat. How do I find out which one is faulty ??? I donr want to have one replaced and then find out it was the other one was the problem.
Also. my mechanic says it is safe to kep driving the car, second opinion please. Apart from the light being on, there are no other related problems with the car, no spluttering, misfires etc.
The car is a 2001 Nov 1.6S 16v Engine code ( AZD ).
Thanks for any replies.

[phil miller]

hi mate the sensors can be tested and checked which should help in replacing the correct one, it may also be worth have the emissions checked because ive had in the past a fault simalar to this and it was infact the cat, what was happening was the cat had failed so the emissions leaving the cat was out side of the limits thus making the lambda sensor give reading the ECU thought were false so it throw up the lambda sensor was at fault, it may save you a few pound just checking this first, hope this helps mate

[Crasher]

The only way to know is by the fault code your mechanic read, this will say sensor 1 or sensor 2.

[VAGMAN54]

if 2 lambdas are fitted and the cat is gone a fault code of p0420 is flagged showing cat below effiency but it is still worth checking the sensors out,if you have a scanner to plug in look through your actual data and see if the sensor is capable of working by introducing an air leak or clamping the fuel return line either way should make it do something if its capable of working that is..............

[belfastmark]

Thanks to all who replied to my post.
It turned out to be the sensor before the cat.
After paying £181, she is back on the road until the next time.