Cancelling Diagnostic Fault Codes After the repair of a troubled area, the diagnostic fault codes retained in memory by the ECU must be cleared by removing the fuse "EFI 15A" for 10 seconds or more, depending on ambient temperature (the lower the temperature, the longer the fuse must be left out) with the ignition switch in the OFF position. Clearing the memory of the ECU can also be done by removing the vehicle battery negative terminal, but in this case, other memory systems (clock, radio etc...) will also be cleared. If diagnostic fault codes are not cleared from memory, they will be retained by the ECU and appear along with any new codes in the event of any future malfunction. If it is necessary to work on any engine components that require removal of the vehicles battery, it is recommended that a diagnostic check is first carried out to identify if any diagnostic fault codes are stored before the ECU memory is cleared. After clearing the memory of the ECU, perform a road test of the vehicle to check that no further malfunctions have been detected and then check that the system normal code is read from the "CHECK" engine warning lamp. If any of the previous diagnostic fault codes have appeared, it will indicate that the troubled area has not been repaired sufficiently. taken from tgtt so its thanks to them mate