Yes a bad checksum*** can (and usually does) stop the car from running. That is the whole point of the checksum. It is the PCM's way of determining if it is "brain damaged". If the checksum is bad then some or all of the data in the PCM is corrupt. In that case the PCM has no way of knowing if any of its calculations are correct. Usually it puts the PCM into limp mode and/or won't let the engine start.Originally Posted by LT1WIRING
Normally if a tuner deliberately chooses not to correct the checksum after modifying the PCM, (usually because they don't know how or do not have the tools to generate a new checksum) then the tuner will disable the checksum. That means the PCM will ignore that the checksum does not match the data in the PCM. It also means that the PCM will never detect any faulty/failing memory. So strange and weird errors can occur and the PCM will never detect them. You could end up chasing phantom problems for weeks or months in that case.
*** Technically it is not the checksum that is bad - but the data that is being checksummed that is bad/corrupt. If you *know* that the data in the PCM is correct, then using EFILive you can regenerate a checksum for that data. EFILive will not let you flash the PCM if the checksums are incorrect.
Regards
Paul
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