Daughters Fiestas eml light came on last night. Put the code reader on today, P0030 fault. O2 sensor. Two questions, are the cheap replacement sensors from eBay worth it or are they rubbish? What size sensor socket do I need to get it out? 

Have you checked connector is ok? I have not bought one since about 2007 so don’t know about quality of eBay ones. Don’t know socket size. Last time I changed one I used ring spanner as wires on sensor stopped me using socket

I just got an £11 one from eBay, took 3 days to arrive and works perfectly.  They are 22mm.  A lambda socket would have made the job easier but wasn't a bad job really 

4 hours ago, isetta said:

Have you checked connector is ok? I have not bought one since about 2007 so don’t know about quality of eBay ones. Don’t know socket size. Last time I changed one I used ring spanner as wires on sensor stopped me using socket

Can’t get a ring spanner onto it, lambda socket is only a few pounds 

53 minutes ago, Paul Smifff said:

I just got an £11 one from eBay, took 3 days to arrive and works perfectly.  They are 22mm.  A lambda socket would have made the job easier but wasn't a bad job really 

Looked at the eBay offerings, a few different sizes. Cheers for the info

I didn't have a lambda socket at the time so cut the cable off the broken lambda and used a long 22mm socket.  Then put the new one in by hand and used a normal 22mm spanner, open end pushing down at a slight angle to do it up tight.  Took a bit of patience as could only turn a tiny bit at a time.

£6 or so for a Lamba socket, I’ll just get one or make my 22mm one into one! Grinder at the ready! 

If you open up a ring spanner end, what's left might just flex (open up) and slip. Better to get a proper Lambda socket which is much more chunky.

he might have meant he will grind a hole in side of socket to put the wires through. should work if the socket is deep enough

I was meaning grinding a socket. Have ended up buying the proper socket, £5.99 free post

Ended up buying three sockets, the one I needed is specific to Ford. It is the right size to take the old sensor out but is to short internally to put the new one in. Lucky I bought three! Anyhow, the old sensor was in tight, very tight. Two foot breaker bar and a 14 stone man giving it large got it to move. Internal threads were ok, so new sensor went in easily with a bit of high temp grease on the threads.