Emissions light and slightly low MPG - Pre or post cat lambda?

[ScarySquirrel]

Hi all,

For the past couple of months I've had slightly lower than normal MPG, at the end of a tank it's usually around 32MPG, whereas normally it'd be about 34 or so. Nothing major, and I've just put it down to being winter really.

Last week I had some work done to mod the cat to a 2.5" exit with a straight through pipe (centre silencer removed) to my Milltek back boxes. All is good, except last night the emissions light came on. Now, the cat is still in place so I don't believe this should be happening.

Based on the above, do you think I need to replace one/both of the lambda sensors? I have no other symptoms, and the car is driving brilliantly.

Thanks

 

[ScarySquirrel]

Any ideas anyone? Shall I just leave it?

 

[daddycool]

swap them around, see if it makes any difference

 

[ScarySquirrel]

It has randomly gone out now, so I guess the lambda sensors are ok. Could a certain type of fuel cause this?

 

[Tom@JMS]

As per Pm, you've got a fault code ; get it checked - no more guessing game!

 

[Sash]

ScarySqwerl clear your PM's!!

 

[ScarySquirrel]

PMs cleared