The solder pad cracking on the relay has been going on for years. That's due to the relays being located in the engine compartment. It has nothing to do with the engine vibrating excessively.
The relay is a big, heavy object held to the circuit board by a solder pad. Even a little vibration causes flexing in that solder joint, something called high cycle fatigue. Solder is not a mechanical joint, just an electrical one, and the metal forms micro-cracks. Also, the temperature under hood can get pretty nasty, and in the winter, the temperature swing can be pretty big. Things expand and contract when they get warm and cold, but the amount and rate depends on the material. So due to differential expanion due to temperature swings (not absolute temperature), there is more flexing stress on the solder pads.
This is a pretty common problem over time. PUtting the relay in the engine compartment is a more stressful environment than behind the glove box. But it doesn't take a massively vibrating engine - just like water erosion of a drop at a time, all it takes is temperature swings and constant, low-level vibration.
In the end, the solution is the same - replace or repair the relay.
posted by 192.249....
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