Cummins 4921776 ECM is a useful part number to search. Good start. Still, I would not buy only because the title has 4921776 in it.
For a quick cross-check, review Cummins Compatible, 4921776 Cummins Engine Control Module and product catalog.
The old ECM label should show the number clearly. If the buyer has a blurry photo, take another one. If the number is on a paper record, send that record too. A clear old label is better than ten messages saying it should be the same.
For Cummins, ESN matters. CPL helps when available. Engine family names like QSB or industrial diesel engine point in a direction, but they do not finish the match. Same family can have different versions. I know that is annoying. Buyers want a quick answer. The ECM does not care.
Connector photo comes next. Check pin layout, plug damage, oil, corrosion, broken shell, or any sign that the harness has been fighting the module for a while. If the old ECM failed from water or harness damage, a replacement may suffer the same way.
A generator-set buyer once asked for 4921776 after checking the old label. That was a much better request than just saying QSB ECM. With the label and ESN, the supplier can check the version and machine use. Without them, the answer is mostly guessing with a nice product photo.
If you are asking for price, send old label, connector side, engine serial, CPL if you have it, and equipment type. Generator set, excavator, truck, marine unit, industrial engine, whatever it is. Short message is fine. Clear evidence is better.
Maybe this sounds too careful for one ECM. I would still do it. A wrong Cummins ECM can mean freight cost, waiting time, and another round of diagnosis. One extra photo is cheaper.
