Yesterday, after driving on the highway for about 15 km, the speedometer starting fluctuating. No other problems. About 4 hours later, we started the car (no problem), but the speedometer was dead. As we continued, the check engine light came on. And then the speedometer started working again. I should add that we leak oil, but the mechanic told us that considering the age of the car, it would be very expensive to fix, and it is cheaper to check the oil regularly and add it accordingly. So, when the engine light came on, we pulled over ( we'd been driving for 2 minutes), checked the oil, which was quite low. ( But we had been driving... ) So we added a little oil and then started up again. The car ran fine and the speedometer kept working, but the check engine light is still on. We only drive once a week and in 6 months have put only about 1200km on it. It does make a bit a of rattling noise when we first get it started and running, but it does not affect the way it drives. We planned to ride this car to the end, before replacing it. What could the problem be? Will it be expensive to fix? ( I want to take it to the mechanic looking a little more knowledgeable rather than having no clue)

Check for codes:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-6.html#post832012

Based on the codes that were thrown, they should tell you what is wrong. Come back and tell us what codes you found and we can go from there.

The Variable Speed Sensor (VSS), located on the transmission (close to the firewall) may be bad (Code 17). The VSS drives the speedometer. Easy job to replace.