Replacing a Lambda Sensor?

[georgemac]

Daughter's Mini One has emmissions light on. Faulty Lambda sensor confirmed by main dealer. Very expensive to replace at dealer - circa £250 already on top of quite a large repair bill for power steering pump/hose and engine mount.

A lambda sensor can be bought for just over £60 from lambdasensor.co.uk but I have never changed one, seems quite easy as long as it comes out OK, that is the unknown, and also what is unknown is if it is the front or rear sensor that is faulty.

Does anyone know which sensor, front or rear reports to the Engine management system, the car is running fine so don't think it would be this one which is faulty.

I could buy 2 sensors for half the price of the BMW repair?

Any advice?

[georgemac]

Car was MOT'd yesterday, have not had time to look at the sensor yet, was half expecting it to fail emmissions test. Passes - results

Fast Idle
CO = 0% - Limit is 0.30%
HC = 8 ppm - Limit is 200 ppm
Lambda = 1.01 Limits are 0.97 - 1.03

Natural Idle
CO = 0% - Limit is 0.50%

I have read on the forum that if getting erratic emissions warning light it may be worth replacing the air filter so this is what I am going to try first, before tackling sensor.
Have also read that the service interval for sensor replacement is 100,000 miles.