exhaust sensor

[cilgwynbaby]

Hi

I was on my way to the in-laws the other day & started to hear a knocking coming from under the car.Had a quick look & there was a sensor had come loose from the exhaust .There were no warning lights on the dash and the car was going fine , so when I got to the inlaws I took it to a local exhaust place for a quik look. They pushed it back in & the cars still going fine.

I have a picture of where the sensors come from & wondered if some one could tell me what it is & the likely cost of having it replaced. hope I have done this right

Thanks Steve

[Britprius]

The sensor should have some wires going into it so it will need replacing. It is used for monitoring the exhaust gas so the the engine ECU can adjust the amount of fuel injected to make the engine run as cleanly as possible. It is very likely that the engine light will come on.
I believe the sensor is about £70 plus fitting.

John. 

[The-Acre]

As John says, it's an exhaust (O2) sensor.  Possible cat damage in the long term if not replaced.  It's dependent on which sensor it is and where the connection is that'll determine how easy it is.