ECU Details

Overview of the VR-4 ECU

MH7201

Early VR-4 (1996-1997) used a MH7201 based ECU

M16C ECU technical notes

Item	Details	Notes
CPU Architecture	M16C	M16C processor family
Flash memory/ROM size	128KB	This is the entirety of the code required to operate the ECU, including the executable code (the software) as well as the fuel and ignition maps.
Processor speed	16Mhz
Re-flash capability	Yes*	While 7201 based ECUs can be remapped, it requires additional software such as MMCflash.

MH7202/MH7203

H8 ECU technical notes

Item	Details	Notes
CPU Architecture	H8 (7202/7203)	H8 processor family
Flash memory/ROM size	128KB	This is the entirety of the code required to operate the ECU, including the executable code (the software) as well as the fuel and ignition maps.
Processor speed	16Mhz
Re-flash capability	Yes*	Most development for VR-4 ECU was for H8 based ECUs. 7202/7203 based ECUs can be remapped with ECUFlash. Early H8-based ECU had processors that were silkscreened as a H8, rather than MH7202/MH7203 and can be read by ECUFlash, but cannot be written to without MMCFlash.

Why are these ECUs still functional?

For the same age and time period, the VR-4 ECU has proven to be extremely reliable, and many 20+ year old boards are still functioning well. In comparison, ECUs of similar vintage from Toyota and other manufacturers are known to suffer from failures due to capacitors leaking. There are no hard rules on when old circuit boards or chips fail, but it is likely that Mitsubishi chose well in regards to CPU and other chips, as well as high quality capacitors.

Location

under heater box, sitting on top of tailshaft tunnel.

ECU Variants

Over the production life of the VR-4 ECU, there were some updates to the hardware which impacted the ability to flash the ROM.

Mitsubishi Part Code	Processor Type	Circuit Board ID	Notes
MD340289	MH7201FS	JE331B132C
MD340288	MH7202F	JE331B154C
MD362895	MH7202F	JE331B154D
MR578135	MH7203FA	JE331B33802B