Electronic Control Module (ECM): Prom

To allow one model of ECM to be used in different vehicles, a Programmable Read Only Memory (PROM) is used. The PROM is a replaceable chip located inside the ECM and contains information pertaining to the vehicle's weight, engine, transmission, axle ratio and other powertrain related variables. The PROM is very specific and must be used with the correct vehicle. Some models may also contain a fuel back-up chip referred to as a CALPAC. If the ECM or the PROM were to fail, the CALPAC contains circuitry which would enable vehicle to be driven in for service.