Why is the car vibrating when it reach 80km/hour

If you can, get us codes so we can help you more.

Before you move forward, check your tires. If they are on the older end, they may be unbalanced or require replacement.

The first thing I would do is a shock test -- press on one side of the car and then release it. If it bounces a lot, the shocks on that side are worn out. Youll want to do this on all four sides of the car. Now, granted, this is a Honda, and the shocks tend to hold up fairly well on most Japanese cars until you rack up 150-200k miles, but I'd still check, as that's not a universal rule. But at the same time it's very common for that to hold true.

The next thing I do is open the hood and check to see if the engine is stable; if it isn't, that can point to faulty engine mounts. The engine might shake a BIT, but it should also realistically be very little. I have also done an engine rev check up to 2-3k RPM as a way to quickly check for things like a misfire that's subtle enough not to trip the CEL. You don't have to rev the motor if you do not want to, but if you can do so, rev it a few times and see if it is consistent, or you rev it once or twice, and it's a bit unstable the first time, but the 2nd and 3rd revs are stable. IF the revs are unstable, it's generally an ignition coil or spark plug issue many times.