Guys, disconnecting the battery used to work with older technology (prior to Bosch LH2.2) which was the first mainstream 'adaptive' ECU. It introduced E2PROMS to motor manufacturers and where before an EPROM can be reset by disconnecting the supply voltage an E2 (written as EEPROM for Electronically Erasable) is as the name suggests a PROM that has to be electronically overwritten. Disconnecting the feed on later systems may well put the light out but will not delete any stored fault codes or in fact reset the system. The adaptive function has both long and short term adaptivity (trim) and it's just the short term that reverts to manufacturers map settings....the long term fuel trim needs to have the code read and then reset (assuming there is just a rogue code or the problem has been fixed) to set the system back to standard again. This is true for the Ford EEC family of ECU's as for other manufacturers. When these later systems were first iintroduced we (Volvo) were inundated with customer complaints where MIL lights were coming on, cars were taken to dealers, the battery disconnected and the car handed back only to have the light come on again shortly after, this was because there was an actual fault and the car had not been fixed and the ECU had only been partly reset. Just for info chaps, lots of information on websites on this if you want further reading but also why I suggested getting a cheap code reader, for around the cost of 3 gallons of fuel its worth having in the car, takes less than 5 min to reset!
