If I change data in PROM, do I need to change checksum??

[David A. Cooley]

At 01:29 PM 11/30/98 +1200, you wrote:
>
>
>
>
>  generally, do ECU's check the checksum of the PROM data before starting
>  and not start, or go into limp mode if checksum is incorrect???
>

Some...
Seems the 94 and up non-obdII Buick/olds/pontiac 3800 V6 doesn't use a
checksum...

On the older ECM's however, there is generally a checksum and if it doesn't
match a "bad eprom" trouble code is set and it goes into limp home mode.

>  .... if so, where is the checksum generally stored on PROM, over what
>  range is it calculated, and what algorithm is used??? is it just a 16-bit
>  XOR??

It's usually the 2's compliment of the sum of all the data *Excluding* the
checksum itself.

Later,
Dave

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