Detection Condition

WARNING: This page is about a different car, the 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0603 and P1605 indicates PCM has experienced a power interrupt in Keep Alive Power (KAPWR) circuit or an internal memory test failure. However, there are external items that can cause this DTC.
DTC P1633 indicates KAPWR circuit has experienced a power interrupt.
DTC P1639 indicates PCM programmable parameters are corrupted or not programmed correctly.

PCM receives information from a variety of sensors and switch inputs. Based on strategy and calibration stored within the memory chip, PCM generates an appropriate output. The system is designated to minimize emissions and optimize fuel economy and driveability. The software strategy controls basic operation of engine and transmission, provides OBD-II strategy, controls Malfunction Indicator Light (MIL), communicates through the Data Link Connector (DLC), allows for Flash Electronically Erasable Programmable Read Only Memory (FEEPROM), provides idle air and fuel trim, and controls Failure Mode Effects Management (FMEM).