Hi all, my ford fiesta mk6 has a fault and after plugging it in its something to do with lower lambader sensor (sorry about spelling). just wanting ideas as garage just said my cats broke but looking i think it could be faulty sensor, break in the exhaust possibly in the flexi section. oppinions needed please before i start buying bits.

Not wanting to state the bleedin obvious, but if my code reader said I had a faulty lambda sensor and I had a break in my flexi pipe then those are the two bits I would buy and replace.

I had a fault with my Toyota earlier last year, management light came on, the garage suggested that my coils where shot and then the lamda sensors were at fault, very expensive. What I wound up doing was taking the induction system apart, cleaning all the sensors in there with an aerosol carb cleaner putting it all back together, it's been fine ever since cost --just a couple of quid.
It may work for you as the testing only tells you a sensor is not doing it's job not why it isn't. Defo worth a try. Just don't touch the sensors with anything except the spray-- they are very fragile.
Good luck.

You need to know what the fault code number (DTC) is, it could be a DCT relating to the sensor itself and its wiring or DTC relating to catalyst efficiency

The downstream lambda sensor is fitted to check that the cat is working but if the fault code is triggered it doesn't mean the cat is broken.
The fault code is triggered when the downstream lambda sensor output follows the output from the upstream lambda sensor too closely then the fault code is triggered.

This can be for any number of reason so the first thing to is look at the live data output from the upstream sensor and check if the engine is running closed loop.
Normally in closed loop running the output upstream sensor should be jumping up and down between about 0.2v and 0.8v about twice a second.

If the voltage output from the upstream is not jumping up and down then the engine is not running closed loop and the reason for this has to be found and rectified.

The downstream lambda sensor should show a fairly constant voltage it should not jump and down
If when the engine is warm and running closed loop the downstream sensor output is jumping up and down following the upstream sensor then the cat isn't doing its job it could be the cat is broken.

[Edited on 2/4/12 by britishtrident]

Thankyou all for the replys i think after checking the exhaust for leaks i will be back to the garage for another check to get all readings and code name/numbers. I will let you know my findings thankyou again.