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 ret