Hey, been using the forum as a fantastic resource for a while now, letting me fix bits and pieces on my car, although I've decided to join and start posting!

About 8 months ago my engine fault light came on. I got it checked out and the rear lambda sensor was reading high. I left it, and now with my MOT coming up, really need to get it fixed. I took it to Ford and they say the whole catalytic converter and both front-and-rear sensors will need replacing. After getting the cost (several hundred), I've decided to do it myself, or at least get the parts myself and get an independant garage to fit it.

The question is, how do I know whether it's definitely the whole cat and both sensors, or whether it's just the rear sensor?

I don't own a diagnostics scanner, although I imagine you might need some information from it to work it out, so any thoughts or advice would be fantastic.

Many thanks

FYI, my car is 2003 Fiesta Ghia 1.4 Petrol

If i were you i'd just replace the rear sensor. Then if it does fail on emissions, get the garage to diagnose what they think it is.
Then if you have to change the cat, no money lost.

Easy job to replace. Do it yourself and save some cash. Just disconnect the battery and leave for half an hour or so after doing it to make sure the ECU can re-calibrate

Many thanks, I've just ordered the rear sensor and will give that a go.

Do you/anyone have any reviews on the cheap £15 USB diagnostic units on ebay, and whether it's worth it for this/future jobs?