ok ford people any idea's my engine managment light is on, changed o2 sencor and crank sencor, disconected battery to reset ecu so light goes out, now on first start up and there after the light stays off and wether it idles for a few mins or u drive10 miles it does'nt come on untill you switch off and restart?

 

You read the fault codes?

 

iv done the hold in trip knob on start up to get check thingy on display and when it gets to DTC it says no code ?

 

That only reads cluster related faults, you need a scanner plugged into the OBD port to read engine fault codes.

 

yeah iv made arrangments for that just wondered if anyone could shed some light on it as to why it does'nt come on on first start up ? the car is running fine,emiision wise it smells good and fuel consuption is normal .

 

Its because the ecu uses standard parameters when you start it up because lambda hasnt had time to warm up ect. Once the car warms up, it uses feedback from sensors, IAT, Lambda, ect to control fuelling and spark timing.

Did you change the 1st or 2nd lambda or both. The Mil light will come on if it doesent see the correct change in oxygen content across the CAT.