Audi A4 Limp Mode
 

Hi all
Got a 2005 A4 TDI Sline, driving fine, took the car to have new air filter on, a few hours later emission light cm on dash, car still drove fine, next day drove to work fine, 2 hours later the cars in limp mode with coil light flashing on dash, wont go above 20mphs. Also the brake lights stay on. After looking on forums it was suggested it could be the break light switch this as been replaced by an auto electrician and made no difference, we was then told to send the ECU off to be checked this also came back faultless! The auto electrician is now wanting to check every wiring loom in the car to see if theres a break somewhere. Someone as suggested it could be the brake relay, any one had this problem or an ideas what it could be and also where the brake relay is???

Thanks in advance...