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

[warrenc at advgroup.co.nz]

  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???

  .... 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??

  cheers,
  Warren Crowther
  '91 Rx-7 13B Turbo