I can clarify retrieving failure codes a little; on LX series cards (basically any card with a handset plug that doesn't start with the letter Z, example ZH) function 1 holds the last known vehicle fault. Press Store than the number one, the next numbers you see will be the previous known fault.
On ZX series EV100 cards there is a little more accessible history; Function 1 still holds the last known fault the same as above but you may also use GE Sentry via a laptop to access the last 16 known faults along with the vehicle hours when the fault occurred.
If you would like me to elaborate any further let me know. Any replies via email I will immediately respond to.
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