Ecu Backup Processor

Honda ECUs are engineered with many levels of redundancy. There is a Backup processor (labeled NEC BACK0004 in most OBD0 and Oki 6534 in most OBD1 (??)). The backup processor is resposible for running the car when the ECU has detected a severe fault, as usually indicated by a "solid" CEL. It does not use the full array of sensors that the car has, and is intended to minimally allow the car to move under its own power in the event of a "total" failure of main ECU logic.