User manuals often end up missing in the case of used cars. But unlike modern operating systems, for the most part, icons used as warnings and indicators on motor vehicles, with few exceptions, are standardized across manufacturers. Some vary, with Check Engine either being an icon, or simply called the Malfunction Indicator Lamp, or simply using text to carry its message, as is the case with Service Engine Soon.
The original check engine lamp was seen in the 1970s. Even the Ford Pinto had a warning called 'engine'. Some in the early 80s also had an icon of an engine, the same icon used for an emissions malfunction as is predominantly used today. Back then, it meant that either the charging system was malfunctioning, or oil pressure was below normal, or coolant temperature was too high, and often appeared in instrument clusters lacking oil pressure, temperature or charging system gauges. It intended to clean up and declutter the panel and reduce the unnecessary skeuomorphism of analog gauges or the clutter of warning lights all over the place (I'm joking of course but you can get my point). 
It literally meant to check the engine. More sophisticated vehicles would even shut down and display one saying 'STOP ENGINE' alongside the engine warning if one kept driving regardless. But the issue was that it was vague. Unless steam appeared from overheating, it was hard for most to tell if it was a charging system or oil pressure issue. Since on board diagnostics didn't yet exist, it added to that trouble. People frustrated with this system just opted for the full gauge package instead. 
One could mention the oil can logo used for low oil pressure is about as dated as the floppy disk save icon, yet most know what the warning light means. It's possible most still know what the floppy icon means, even today.
For the record I still prefer my cars basic, familiar and not full of endless warning lights, even though I do drool over that technology seen in many new cars. But I would likely grow tired of the constant nagging just as I used to yank out the buzzer module from my Chrysler Fifth Avenue that sounded if I didn't fasten my belt or left the car with the keys in the ignition.