Hi. Still seem to be having trouble with an O2 sensor on my Mark II 05 Focus (1.6 CVT). It intermittently still plays up in warm/humid weather, and is causing the occasional stall. Trouble is that the engine management light still hasn't come on, and my local ford dealer reckon they can't do anything without the error code because there are several different O2 sensors that it could be. (Well, they have offered to do a trial and error swap around). Is this true?

Surely there must be some way for them to check it?

The car recently passed MOT and emissions were very good.

I'm annoyed and confused with the car and with Ford and I don't want to pay for half-a-dozen different diagnostic checks... Help please!!!

can they not do a diagnostic check with live readings?

can they not do a diagnostic check with live readings?

This is what I suggested but there was a considerable amount of sighing - basically because the fault is intermittent, they are saying they will charge me £80 per diagnostic and say there is no certainty that they will find the problem first time.

This is why I'm annoyed - can any garage do the diagnostics? Or even the AA?

This is what I suggested but there was a considerable amount of sighing - basically because the fault is intermittent, they are saying they will charge me £80 per diagnostic and say there is no certainty that they will find the problem first time.

This is why I'm annoyed - can any garage do the diagnostics? Or even the AA?

Take you business elsewhere, If its a hassle for them then fine!

Most if not all garages will be able to do a diagnostic test, the AA might even be able to help with reading fault codes (not sure what they have)

The AA generic unit is pretty good actually, but I agree take the business elsewhere, by the sounds of it they want to charge you for plugging in the computer, then charge you for changing a sensor, then doing that over and over till they find the right one... Not a bad deal for them £130 per failure to find the fault so I can see why they sighed when you asked for a bit of common sense.

Most places will have some form of diagnostics, ok its not Ford own, but for £25 to plug the car in and get a code, or £80 + vat at your local dealer? No Brainer really!

Cheers for confirming what I suspected...

I've been looking at some US forums, they seem to suggest that the only O2 sensor that would be messing with the engine this way would be the pre-cat sensor, the post-cat sensor would be registering as a CAT problem. Can anyone confirm this, as it might just make sense to replace the pre-cat sensor without worrying about any expensive diagnostics....

Could well be the case, and if you can replace it yourself its much better and cheaper, and may be wirth the gamble. Best thing to do is swap the pre and post cat sensors around, does the error code change...