Tried a few things on the E420 dash.

Read the EEPROM and it only had a few bytes of info, burned that data to another chip, display was completely blank ( no miles, time or temp ).

Read the original chip on a different reader and got nearly 1K of data, put original chip back in , had original mileage but trip odo was at 000.0. Looks like my first reader isn't working properly.

It also looks like one of the MCUs has an EEPROM area to hold miles as the 93C53 data was never altered when I pulled the chip.

There are 2 MCU's on the board:

The one near the 93C53 is marked:

NEC ( maker of chip )
78012BGC739 ( this is a 78012B series MCU )
VDO E540 ( Maker of instrument cluster, E540 looks like a house # )

According to the data sheet I've found, it has 16K of mask ROM ( program built into actual chip when made not after, isn't lost when power is off, can't be changed after chip is made ) and 152 RAM ( used as the program is running, will go away if power is lost )


The second is:

ITT
CDVJ E547 ( E547 looks like a VDO house # )
G45449.001
6113 391/S

I can't find any data on this one.

For comparison, I have a 97 S430 ( dash like the same year SL ) with these chips.

EEPROM
C56M6 ( Looks to be a 93C56 )
27PB

This is close to a MCU marked:
ITT
CDJV-E575 ( E575 looks like a VDO house # )
G48654.002
6234 45/S

I can't find any data on this one.


The other MCU is
Motorola
VDO_E408 ( VDO house number )
0F74B ( I know this is the ROM MASK order # )
LZYC9621 ( this is a line and date code 1996 21 week )

I'm still trying to find out what the red LED below the speedo needle is and what happens when it rolls past 1 M miles. Also, the displayed mileage resides in the inst cluster as the two listed above have different mileages.