DiRT 4

At the current state, this achievement is kinda buggy. For 4 months between December, 2017 and March, 2018 the server just simply didn't register our Weekly Challenge times, no matter how many times you completed both of them. I suggest you to start doing this as soon as you start playing the game!!!

All you have to do is to compete BOTH Weekly Events in 2 weeks in a row. The servers are refreshing on every monday, 12:00 (Central Europe Standard Time) so you can check which tier you finished and you can go for the next Weekly Challenges. On the third week, you should get the achievement. If for some reason it doesn't pop, it mean that one of your times wan't registered, so just keep trying and trying until you get the chivo. It is a pain in the ass, but there is no better solution for this, until Codemasters decide to fix the servers or the communication problem.

Edit: Several people in the comment section says that you only have to complete one weekly event for the achievement. It might be true, unfortunately i cannot confirm it since i already unlocked the achievement. If you really not sure about it i still suggest you to complete both of them. Not just to be a 100% about the completion, but you also earn more credits what you can use to improve your team and garage furthermore.

You do NOT have to complete BOTH. I completed one last week and didn’t even attempt the second and DNF one and finished the other the previous week and the achievement popped for me today

Allow me to provide the definitive guide that clears up the misconceptions from the other guides:

There are two weekly events each week, both start and end at the same time. Call them "Left" and "Right".

You can find the weekly events in Events -> Competitive -> Community Events

You only need to do one of them each week over the course of two weeks.

However

The game will only award you the achievement if you complete the weekly challenge from the same side as the week before.

So for example:

Week 1 - DNF & Success
Week 2 - Success & DNF

This will not grant you the achievement.

Week 1 - Success & DNF
Week 2 - Success & DNF

This will grant you the achievement. I hope this is clear.

I still suggest that you complete both of them, and make sure you finish any active singleplayer championship before claiming your rewards. The achievement will pop after claiming the reward for the 2nd week.

If you are struggling with the driving sections, slow down, you are not required to win the event, you are only required to finish it. Trust in your spotter but exercise caution. Even if you are pushing for tier 1, in the weekly event, you can take the time to go slower, but terminal damage ends it for that week.

One point to note - online achievements are blocked if you have an ongoing career championship. Finishing the event an re-attempting should allow the achievement to unlock.

I happened to attempt this alongside finishing up the game, with the Triple Crown achievement. However, for a few weeks it wouldn't pop. I figured this was because I'd started one of the three Triple Crown events, so it was treated as in progress, and therefore blocked this popping.

I'd completed the Rally event of the Triple Crown, then left the other events for a few weeks. In between, I finished a number of weekly challenges (in various combos - 1 challenge, both challenges etc.). Achievement didn't pop. Then, I completed 2 weekly challenges, finished the remaining Triple Crown events, and then reviewed the Competitive menu to receive my completion awards. At this point, this achievement popped. So it seems that the Triple Crown is treated as one championship