Ford Focus TDCI 2002 - ford focus wont go into learning mode to programme - blondjoe

Hi, Can anybody please help. I have a 2002 ford focus 1800 TDCI. My fob wont work. I replaced the battery & got the fob tested, all ok & the key starts the car. I have tried reprogramming my fob to work the central locking. I get the first noise when i try to programme it, but i dont get the second noise & the light above the clock wont go into learning mode. After many hours looking on net i discovered that it may be GEM fault. I have been told to disconect this & clean it but not sure where it is exactly. It could be behind glove compartment. Can anybody please advise me or tell me what else the problem could be. Thanks in advance