l have a Peugeot 306xl 1996 (P reg). It has a keypad immobiliser. l have just fitted a new engine but it will not start, only turns over. So if you disconnect the battery to fit new engine do you have to use the default code afterwards? if so what is it? Also if you put the wrong code in too many times would this effect anything?

Any help would be very appreciated.

you will have to use the default code but if this doesnt work you are going to have to put it into get te code redone had the same prob only other prob is that it cost a few bob we got a new car traded it in cause it wasnt going to be worth it in the long run all the default codes are diffrent we had about 4 diffrent codes thats when we tok it to the garage it was going to cost so think twice

Fitting an engine or disconnecting the battery will not affect the immobiliser. When you put the code in, does the light still change from red to green? It sounds more like something has not been connected right when fitting the engine.
Default is 1111 if the light is still red.

l disconnected the keypad immobiklliser on mine when this happened was gonna cost a fortune to fix default code is 1111 then take out the keypad and connect wires straight thru my auto electrician was wicked! cost me 20 quid in end

2 things make a car go petrol & a spark

do you have petrol in it , is there a spark at the plugs , petrol pump o k ??

you might have to let the garage test the immobiliser very tricky things when these play up you might not of connected something properly or the chip in the immobiliser might of crashed eitherway pricey .